Open access is a set of principles and a range of practices through which research outputs are distributed online, free of cost or other access barriers. With open access strictly defined, or libre open access, barriers to copying or reuse are also reduced or removed by applying an open license for copyright. Wikipedia In addition to publishing, OA also has implications for data, education and government.
The Scholarly Publishing and Academic Resources Coalition is an organization whose mission is "to enable the open sharing of research outputs and educational materials in order to democratize access to knowledge, accelerate discovery, and increase the return on our investment in research and education. As a catalyst for action, SPARC focuses on collaborating with other stakeholders—including authors, publishers, libraries, students, funders, policymakers and the public—to build on the opportunities created by the Internet, promoting changes to both infrastructure and culture needed to make open the default for research and education." You can find many useful resources on their site https://sparcopen.org/open-access/
As with open access journals, there are different business models for funding open-access books, including publication charges, institutional support, library publishing, and consortium models.
An institutional repository is an archive for collecting, preserving, and disseminating digital copies of the intellectual output of an institution, particularly a research institution.