level editing ('mapping')
1. involves creating (editing) game levels and perhaps some modelling, sound and texture creation.
2. artist only, generally without programming required.
3. practice arguably initiated by Bard's Tale Construction Set and popularised by idSoftware's Quake series.
4. with Quake, the user became a developer. first entry point for user driven, community distributed content creation.
5. Pragmatic to release tools to do this - extends the shelf-life of the game
6. 'Maps' and other art are distributed in an archive format.
7. Creator is copyright holder of the map only. map creator cannot distribute the game with their work.
Suggested engines / editors:
Artistic Level Editing examples