o) What is an "institutional or discipline-specific repository"?

A repository is an information platform (document server) where scientific documents are stored and where research results can be freely accessed from anywhere in the world.

Institutional repositories are based at higher education institutions or other research institutions. For example (non-exhaustive list):

Discipline-specific repositories are document servers where documents pertaining to a particular discipline are stored.

Institutional and discipline-specific repositories are listed in the Directory of Open Access Repositories (OpenDOAR).