A build is a version of the game and each build should include it's revision number (from source code control) and build time. A easy way to make a build is important and one way to do it is to create a build server. It's important to track in what build a bug is reported. The game also often contain a version number that the final user will see and will be updated later with each public release of the game. This can be created a number of ways, the important part is that there is a way to go from a version number to a revision number so one can pinpoint the precise build version used for every crash. There are also these common names given to certain builds or range of builds in the production of a game.
A build delivered to the publisher.
A early pre-production version to test the idea of the game play or technology of the game.
The first version of the game where one can play anything and feel that it is indeed a game.
A vertical slice is a small section of the game done at Beta level quality.
Open up the game for players to play early in development so they can give feedback on gameplay features as well as content.
All content is in the game but all of it is not final quality.
All content is final and only the bugs remain.
When enough bugs has been squashed in a beta there can be an open beta. The goal is to get more player running the game to stress systems such as multiplayer or get the game tested on many more platforms then QA studios have access to.
Bugs have been fixed and this is a version sent of to the one who approves it for final release. If this fails it will be a RC2, RC3 and so on until it's good enough and can be called the Gold Master.
The final build that will be released.