This is a project which contains one class: a Build Bot Project description. Both the BuildBot project depends on it and a project which wants to be build botted should depend on it. So that the project under buildbot knows which interface to implement, and BuildBot can find the current projects in the workspace which can be build by it. For an example: see BuildBtMockProject (just some mock project) and BldBtMockPrjLoader (which is dependent on BBProjectDescription and describes BuildBtMockProject as project which it wants to get build).