What is Open Access? Check out the video below for an introduction.
Gold OA: OA through journals regardless of the journal's business model
Green OA: OA delivered by repositories
Gratis OA: Access is free of charge, but not necessarily free of copyright and licensing. It moves price barriers, but not permission barriers. Users still need to seek permission to exceed fair use
Libre OA: Free of charge and also free of some copyright and licensing restrictions
Repository: a repository is an online database of OA works