In simple terms an institutional repository is a place to store digital copies of scholarly work and make these materials freely and easily accessible.
For an academic researcher it is a place to store, manage and disseminate their work via the World Wide Web. The work can include publications in peer-reviewed journals, books and book-sections, technical reports, working papers, monographs, conference presentations, audio and visual materials or any other research content that has some scholarly value.
A librarian might consider a repository as somewhere to catalogue, preserve and archive digital materials for posterity. This includes enabling easy access to these materials via a simple persistent web address.
A research manager might view a repository as a barometer of an organisations research productivity and health. They might use the repository to inform on strategic planning.
An IT professional might consider a repository as a type of digital asset management (DAM) system. They might see the system as hardware, software and processes for the ingestion, annotation, cataloging, storage and retrieval of digital materials.
An organisation might see its repository as a record of its intellectual assets. The organisation would use the repository to help meet research council requirements, improve its reputation and demonstrate to its employees that their work is valued.