Game Development processes

Game developers may produce the game design document in the pre-production stage of game development—prior to or after a pitch. Before a pitch, the document may be conceptual and incomplete. Once the project has been approved, the document is expanded to a level where it can successfully guide the development team.

Because of the dynamic environment of game development, the document is often changed, revised and expanded as development progresses and changes in scope and direction are explored. As such, a game design document is often referred to as a living document, that is, a piece of work which is continuously improved upon throughout the implementation of the project, sometimes as often as daily.A document may start of with only the basic concept outlines and become a complete, detailed list of every game aspect by the end of the project.

A game design document may be made of text, images, diagrams, concept art, or any applicable media to better illustrate design decisions. Some design documents may include functional prototypes or a chosen game engine for some sections of the game.
Although, considered a requirement by many companies, a GDD has no set industry standard form. For example, developers may choose to keep the document as a word processed document, or as an on-line collaboration tool.

The purpose of a game design document is to unambiguously describe the game's selling points, target audience, gameplay, art, level design, story, characters, UI, assets, etc. In short, every game part requiring development should be included in detail enough for the respective developers to implement the said part. The document is purposely sectioned and divided in a way that game developers can refer to and maintain the relevant parts.
The majority of video games should require an inclusion or variation of the following sections:

Story
Characters
Level/environment design
Gameplay
Art
Sound and Music
User Interface, Game Controls

This list is by no means exhaustive or applicable to every game.