Open Access (OA) is free, immediate, permanent online access to the full text of research articles for anyone, webwide.
There are two roads to OA:
(1) the "golden road" of OA journal-publishing , where journals provide OA to their articles (either by charging the author-institution for refereeing/publishing outgoing articles instead of charging the user-institution for accessing incoming articles, or by simply making their online edition free for all);
(2) the "green road" of OA self-archiving, where authors provide OA to their own published articles, by making their own eprints free for all.
The two roads to OA should not be confused or conflated; they are complementary. (This site is focussed largely on the green road, because it is the fastest and surest way to reach immediate 100% OA; but the green road might eventually lead to gold too.)
OA self-archiving is not self-publishing; nor is it about online publishing without quality control (peer review); nor is it intended for writings for which the author wishes to be paid, such as books or magazine/newspaper articles. OA self-archiving is for peer-reviewed research, written solely for research impact rather than royalty revenue.