FREDFReespace EDitor - The program used to create the original missions in FreeSpace. It's bundled with the game allowing you to make your own missions too.
CampaignThe name for a series of missions which must be flown in order. As opposed to stand alone missions which can be flown from the tech room.
ModA modification of the game. This can be a single new ship, weapon or effect or a collection of them. A large package of mods is usually accompanied by a new series of missions so the term campaign is usually used for these.
SCP - The Source Code ProjectVolition, the creators of FS2 released the source code to FS2. Since then the programmers in the community have been working on it to improve FS2. The changes they have made surprised even the programmers at [V].
FS2_OpenFS2_Open is the result of the SCP's work. A new executable that runs and improved version of FS2.
FRED2_OpenFS2_Open's companion. The mission editor which allows you to create missions using the new FS2_Open functions
PCS - Pof Constructor SuiteThe program used by most modders to convert new ships into a format usable by the game. Check the modding section for more details.
VPViewA program which allows you to look inside the vp files FS2 campaigns (including the original one) usually come in. You can find more details in the VPView tutorial link at the side of the page.
UnRARThe process of using WinRAR (or another extraction program) to unpack a .RAR archive. Rar is similar to the zip format but gives much better compression ratios which means that it is greatly preferred by members of the community to the zip format. Although WinRAR is shareware it only nags at you to register.
BOE or Battle Of Endor SyndromeNamed after the giant space battle at the end of Return Of The Jedi, BOE is the generally derogatory term used for missions that attempt to have too much going on at the same time. The problem with trying to recreate cinematic battle sequences in FreeSpace is that they can often result in missions where the out come is no different if the player simply decided not to participate. A more detailed explanation of the problem can be found here