The typical preproduction period for developing a game is very similar to that of the film industry. It means defining the product! For most studios, going into preproduction means that a great, new game concept is on the table and now it must be pitched and sold to a game publisher. This usually means creating a formidable game design document and either a prototype of the game or a vertical slice of what the game will be like—this is usually a single level of game play that will later be used within the finished title.
Key decisions that determine the quality and cost of the game must be made in preproduction—these choices include the number of personnel that will be hired, the length of the production schedule, ...