A rather nebulous term, I suppose, but a truly fantastic idea. An institutional repository gives professors and researchers a place to post their articles where anyone can access them for free.
California has created a version of this called the eScholarship Repository, which "provides a robust full-spectrum, open access publishing platform for pre-prints, post-prints, peer-reviewed articles, edited volumes and peer-reviewed journals" (quote taken from this UC article). Not only is this open to those in California, but to the rest of us as well. It is also structured in such a way as to be searchable by Google so I have added it to my Free Full-text E-Journals custom search engine (see the right-hand side of this blog for the search box. For more information about this custom search engine, see my previous post).
It is unfortunate in the academic publishing world that professors (and other researchers) very often give up their rights to their own work when publishing in a journal. Once accepted by a journal, that work becomes the property of the journal, not the professor. Many professors do not even think about this loss of rights because they need to publish for tenure purposes. Part of creating awareness of an institutional repository would necessarily include discussion about maintaining one's rights to a work, which is a good thing. The more professors are aware that they need to keep their rights, the more articles can be put in institutional repositories!