Just to throw a spanner in the works, some of the definitions might also class "multiplication" as an engine. The game needs it to work, but it isn''t the game. Multiplication is a core part of the game but it is not the game.

Or maybe I''m just being pedantic

Trying is the first step towards failure.

Good posts guys - I think I''m learning something here

To try and make it a little more clear - I hope this tree structure makes sense?...

(3D) Game

(3D) Game Engine

(3D) AI Pathfinding

(3D) Sound Engine

(3D) Collision Engine (Physics)

(3D) Gfx Engine

Display (3D) Models

Display (3D) Scene

Display (3D) User-Interface

(All 3 above) using OGL or D3D

(Not including data like models, textures, sound, ...)

Looks good, but what is a 3D engine? A 3D Pathfinding Engine?
Sounds oke - but how come when you hear the words "3D engine" you think of graphics? Is this wrong? Why are there so many 3D gfx engines, and so little 3D AI engines?

A game is composed of several modules, or interfaces, such as: Graphical Interface, Audio Inteface, User Feedback Interface(input), Game Data, Networking Interface, Game World Interface, ect... a game engine refers to all of the stated interfaces EXCEPT for the actual Game Data, Initialization code, and other application and client level code. The Game Engine would be the interfaces(functions, Classes) that the game code uses to manage and process all of the games input/output/data storage requirements.

-Brent Robinson