Original: The soundtrack for The Orange Box consists of music that Valve employees composed for Half-Life 2: Episode One, Half-Life 2: Episode Two, Portal, and Team Fortress 2.
Simplified: It has five games on it - Half-Life 2, Half-Life 2: Episode One (an expansion of Half-Life 2), Half-Life 2: Episode Two (another expansion of Half-Life 2, Portal, and Team Fortress 2.