APC: Article processing charge or author processing charge. This fee is typically paid by the author or the author's institution to compensate the publisher in lieu of subscriptions.
BPC: Book publishing charge, paid typically by the author or institution to compensate the publisher.
CC: Creative Commons. A freely available license that can be attached to any open access publication that dictates what a user can do with the publication besides simply viewing: attribution required, non-commercialy use only, etc.
DOAJ: Directory of Open Access Journals. The premier list of open access journal that go through a vetting process (all must, for example, show evidence of peer review) before appearing in this directory.
Green OA: Archiving by an author or institution on a website or institutional repository by an author or institution the pre-print or post-print of an article. This practice is generally authorized by publishers as a means for broader access to an author's scholarly work.
Gold OA: A journal that publishes open access, meaning that all the articles are immediately available for free.
Hybrid OA: A journal that is partially subscription-based, and partially OA (articles funded through APCs and then published as OA).
Postprint: The post-peer reviewed version of an article, before it is formatted by the publisher. It is this version that is most often archived in Green OA repositories.
Preprint: The pre-peer reviewed version of an article, that may be included in a repository or other self-archiving platform depending on the preference of the author or archivist.