Sega games have been around for quite some time, and in many different regions.  As you tend your garden of Sega and watch it grow, there will likely be a time when you come across some term you're not familiar with.  As each Sega system is different from each other, often the terms used for different systems and regions may differ as well.  I've compiled a small glossary of some of these terms here to help you sort out what's what.  These are by no means comprehensive entries - you can always do a search on Google or Wikipedia if you want more information on any of them.  I've decided that alphabetically would be the most convenient way to organize this list, so here you go:

4-IN-1 - A reference to the EMS Action Replay cartridge which provides four separate functions, as follows: (1) Region bypass, allowing you to play games from any region; (2) Cheat device, allowing you to enter and save cheat codes for your games; (3) Backup memory (though it is not direct-save memory accessible within the game, you can only copy from the Saturn's internal memory to the cartridge); and (4) Expansion RAM to play the SNK or Capcom games that required additional memory.  Early 4-in-1 carts had 1 Megabyte of expansion RAM.  When Capcom started releasing games that required the 4 Megabyte cartridge, EMS upgraded their cartridges as well to run them.  The upgraded cartridges are sometimes also referred to as 5-in-1 cartridges (treating the 1 MB expansion ram and 4 MB expansion ram as two separate features).

CERO - Acronym for the Computer Entertainment Rating Organization.  CERO is essentially the Japanese equivalent of the ESRB, and they put age ratings and content descriptors on video games released in Japan.

CINEPAK - A video compression technology widely used on many Sega Saturn games.

CR2032 - This is the size of the oh-so-versatile battery used for Dreamcast VMU's, the Saturn's internal memory, and even many Genesis games that used battery-backup!

DATING SIM - A primarily Japanese genre of video game, where the player's goal is to get with one or more women, usually with multiple endings depending on which girl the player decides upon by the end of the game.  These can be relatively clean, or at the opposite end of the spectrum, and likewise can be anwhere from sweet and romantic to... well... more than a bit "rape-y."  In order to differentiate themselves from other games in the genre, some games will also mix in another genre (or focus on it primarily, with only a minor focus on the dating sim aspect), such as a racing game, or a strategy game, etc.

ENQUETTE - Enquette refers to the small questionnaire that is included with many Japanese video games, that can be filled in and mailed back to the publisher.  It is essentially the same sort of thing as a registration card that is sometimes included in US games (though the trend nowadays is more towards online registration).

ESRB - Acronym for the Entertainment Software Ratings Board, the group that puts the age ratings and content descriptors on games released in the US.

FMV - Stands for Full Motion Video.  Hailed by the mass media as the future of video gaming when the Sega CD first came out, games that were based solely on Full Motion Video have thankfully all but died out now.  FMV is still used in many games today, but usually only for cutscenes in the game, not during actual gaming sequences.  Its use has become a lot less common with advances in 3D graphics, since developers often simply choose to use the game's engine to render the cutscenes.

GREEN LABEL - Green Label refers to a content rating on Saturn and older Dreamcast games.  The term "Green Label" comes from the color of the small box on the front of Saturn games and the small strip on the back of Dreamcast games deemed appropriate for all ages.  The Kanji shown in the box/strip is 推奨年齢　全年齢, which non-japanese speakers have a difficult time pronouncing, and so people just refer to the label by color.

HIRAGANA - Hiragana is a syllabic alphabet that can be used to write words, particles, etc. in Japanese.  Hiragana can be used to spell out Kanji for people who do not know a particular Kanji character.  Hiragana is largely reserved for words of Japanese origin.  For most adapted foreign words, you would instead use Katakana to write them.

KANJI - Kanji is the most complex of the three main forms of written Japanese language.  Unlike Hiragana or Katakana, which are essentially fixed transcriptions of syllables, Kanji can mean different things depending on whether and what other Kanji it is combined with, and can also be pronounced radically differently.  There are roughly 2000 "standard" Kanji characters that Japanese readers are expected to know.  If you play Japanese games, you will doubtless run into quite a bit of Kanji, particularly with RPGs.

KATAKANA - The simplest of the three main forms of written Japanese language for Americans to understand, Katakana is essentially a syllabic alphabet used largely to transliterate foreign words into Japanese.   Thus, once you learn katakana, you can often understand what the word you are reading is by sounding it out.  For example, アダプター, which could be written in romanized letters as adaputaa means "adapter".  Many times in Japanese games, menus, options, and even items are written in English or Katakana, so many times, a non-japanese speaker can have a great deal of enjoyment with a game just by understanding Katakana.  The more complex a game is, the more likely a non-japanese speaker will have difficulty though.  Fighting games and shooters are generally quite import-friendly, but RPGs and dating sims are usually very heavy on the Japanese.

OBI - also often called "Obi Strip" or "Spine Card," the Obi is indiginous to the Japanese region.  The Obi has been on Japanese books and music CDs for ages, so it was only natural for it to migrate to games which, like CDs, came in jewel cases during the Saturn and Dreamcast era of gaming.  At that time, pretty much all games had a little strip of cardboard that wraps around the spine of the case known as an Obi.  The cardboard strip contains the UPC code as well as other miscellaneous bits of information (the game title, the system it's for, etc).  There are, of course, exceptions, such as for promitional games like Christmas NiGHTS which were never actually sold at retail.  The word Obi originates from the sash used to tie a Kimono.

PEGI - Acronym for Pan European Game Information, which is Europe's equivalent to the ESRB, putting age ratings and content ratings on video games released in Europe.

PORT - A conversion of a game for a console, usually from the arcade (such as Virtual On for the Saturn), though sometimes the port can be a conversion from a competing console.  Sometimes the port is better such as Soul Calibur on Dreamcast versus the arcade counterpart, sometimes the port is practically identical, and sometimes the port is of inferior quality such as Alien Trilogy on the Saturn.  Port also refers to the various slots or plugs where you would insert cartridges, controllers, etc. to use them.

PRE-RENDERED - The concept of pre-rendered graphics is to give the illusion of 3D while still actually using 2D sprite-based technology.  This is seen fairly often in Saturn games, and even some Genesis games.  How it works is that a 3D model is created, and pictures are taken of that model in various poses, which are then used and animated as sprites.  One example of this in action is Virtua Fighter 2 on the Genesis.  The Saturn and Arcade versions of Virtua Fighter 2 rendered the characters in 3D on the fly.  The Genesis, on the other hand did not have the processing power to render highly detailed 3D polygonal graphics (or DID it?).  Thus, when the game was released on the Genesis, instead of 3D, the graphics are pre-rendered sprites.  Another good example is Shining the Holy Ark, which uses pre-rendered graphics for characters and enemies, but the backgrounds and such are actual 3D polygons.

RED LABEL - Red Label refers to a content rating on Saturn and older Dreamcast games.  The term "Red Label" comes from the color of the small box on the front of Saturn games and the small strip on the back of Dreamcast games deemed wildly inappropriate for people under the age of 18 (Very graphic blood and guts, or heavy sexual content, including nudity).  The Kanji shown in the box/strip is Ｘ指定　１８才以上.  Since most of the games released at the time were the "Green Label" games appropriate for all ages, the other two classifications were referred to by their colors as well (Yellow and Red).  The difference between Red Label games and Yellow Label is the severity of the content.  A Yellow Label dating sim might have panty shots, and sexual sounds, but a Red Label dating sim, on the other hand, could have full nudity).

REDBOOK - This refers to standard CD Audio tracks that are sometimes found on CD-based games.  Many times game would have all the actual game music right there as tracks that could be played in a normal CD player.  The game would load the data to play the game into memory, then stream the soundtrack right from the disc.  Redbook in games pretty much disappeared once games abandoned the CD format for DVD.

SPINE CARD - also often called "Obi" or "Obi Strip," the Obi is indiginous to the Japanese region.  The Obi has been on Japanese books and music CDs for ages, so it was only natural for it to migrate to games which, like CDs, came in jewel cases during the Saturn and Dreamcast era of gaming.  At that time, pretty much all games had a little strip of cardboard that wraps around the spine of the case known as an Obi.  The cardboard strip contains the UPC code as well as other miscellaneous bits of information (the game title, the system it's for, etc).  There are, of course, exceptions, such as for promitional games like Christmas NiGHTS which were never actually sold at retail.  The word Obi originates from the sash used to tie a Kimono.

SPRITE - a movable 2D character or object in a video game.  In Golden Axe, for example, all the heroes, all the enemies, the little gnomes, the magic pots, the spells  themselves, etc. were all sprites.  Sprites are animated in a similar way to traditional cel animation - by sequentially replacing the currently visible image with a slightly different image.  As each frame of animation requires a new sprite, high quality 2D animation in games can require a lot of memory and a lot of processing power.

TRUEMOTION - TrueMotion is a compressed video format used in many later Sega Saturn and some Dreamcast games.  TrueMotion provides significantly higher quality than the Cinepak format that most Saturn games used for FMV.

TWINSTICK - This refers to the special controller released for the Saturn and Dreamcast to properly play their respective iterations of  Virtual On.  The controller consists of a wide base with a start button in one corner and two tall digital 8-way joysticks protruding from the top of the base on opposite sides.  The sticks each have a thumb button on top and a trigger button on the front.  The Dreamcast stick also has a button on the base right between the two sticks (which can be used to perform some special attacks).  There is an adapter available to make the Saturn Twinstick operable on the Dreamcast (although the moves accessible by using the middle button are not available that way).  Whichever you choose, it really is the ONLY way to play Virtual On.

VMU - VMU is an acronym for Visual Memory Unit, the standard Dreamcast memory card.  It fits into the Dreamcast controller and has a screen (hence the word "Visual") that is sometimes used to convey useful information.  Taken out of the controller, it can be used on its own to play mini-games that have been loaded onto it.  Its flash-based memory can hold an underwhelming 128KB of memory.

VMS - It's what the VMU was called in Japan.  Because they had to be different.

YELLOW LABEL - Green Label refers to a content rating on Saturn and older Dreamcast games.  The term "Yellow Label" comes from the color of the small box on the front of Saturn games and the small strip on the back of Dreamcast games deemed appropriate for people age 18 and over.  The Kanji shown in the box/strip is 推奨年齢　年齢制限　１８才以上.  Since most of the games released at the time were the "Green Label" games appropriate for all ages, the other two classifications were referred to by their colors as well (Yellow and Red).  The difference between Red Label games and Yellow Label is the severity of the content.  A Yellow Label dating sim might have panty shots, and sexual sounds, but a Red Label dating sim, on the other hand, could have full nudity).