As I understand the term it's someone who inherits the feature-complete codebase after the original author left it. The duty of such a programmer varies depending on the place and project, but it's generally someone who will be asked to fix the bugs and implement new features should the need arise.

There's nothing derogatory to the term, although it's good to have some sympathy for such people - enough not to write bad code when first coding the project in the first place.