There are many terms that are specific to Xbox Gamerscore and achievement hunting, so I've put together this glossary of terms for anyone who might be confused when we refer to a "stack", "boosting", or getting a "1K".

Glossary

• 1K - Complete the base gamerscore in a game, typically 1000 points, thus 1K. Sometimes used to refer to a completion in general.
• Achievements - see Cheevos
• Bean Dive - Annual challenge on TrueAchievements.com aiming to earn at least one achievement in every game in your backlog, coined by it's creator, Beanpotter. The "dive" refers to the loss of completion percentage as a result of starting many new games.
• Boosting - Using gameplay mechanics specifically to unlock achievements. Generally refers to the act of setting up multiplayer matches in particular ways to perform achievement criteria without interruption from regular players. Working towards achievements in lieu of regular gameplay.
• Cheevos - see Achievements
• Discos - Discontinued achievements - achievements that are no longer unlockable, probably due to online server shutdowns
• Gamerscore League (GSL) - An annual gamerscore competition hosted on XboxAchievements.com
• Great Random To Do List Challenge - A contest run by Facial La Fleur on the AchievementHounds.com community forums
• GTASC - The Great True Achievement Score Challenge, a year-long, weekly elimination contest run by planting42 on TrueAchievements.com
• Knobs - Unobtainable achievements - achievements that have never been unlockable due to a bug or some other issue
• NTSC - See NTSC-U
• NTSC-J - One of the three regional variants of Xbox 360 consoles, mostly associated with Japan, Korea and other countries in that region. Also see Region Locking, NTSC-U and PAL.
• NTSC-U - One of the three regional variants of Xbox 360 consoles, mostly associated with North America, Canada, Mexico, and other countries in that region. Also see Region Locking, NTSC-J and PAL.
• PAL - One of the three regional variants of Xbox 360 consoles, mostly associated with Europe, Australia and New Zealand. Also see Region Locking, NTSC-J and NTSC-U.
• Potentially Endless Bean Dive - A contest created on the AchievementHounds.com community forums that requires starting a new game every day. Began on the 28th of February 2013, and still going.
• Preloading - The act of working on the criteria for an achievement until it's almost unlocked, and saving it for a later time, usually for competitions.
• Ratio - Generally refers to the rarity of an achievement as determined by numbers of players of a game vs number who've unlocked the achievement. A statistic calculated on the TrueAchievements.com website.
• Region Locking - Games can be locked so they only play on specific region consoles. See NTSC-U, NTSC-J and PAL.
• Stack - Sometimes a game is released in multiple versions, for example in different regions or on different platforms, and in these cases they can have an entirely independent achievement list. To "stack" a game describes earning the achievements on more than one version of what is, in gameplay terms, the same game. Examples: Batman: Arkham Asylum and Bioshock
• TA - True Achievements, either the score type or the website TrueAchievements.com