Beta is the word where a certain piece of software is closed to the public. A few people is added with the staff members to test the software before it is finally released to the public to use. For example, ArmorGames Version3 is currently in Beta form before it will shortly become Public.
Then you've probably heard in videogaming where they are releasing Gears of War 3 beta keys. These keys are usually codes given to the players that want to play the game before it becomes a game.
