Open Access Journals

Open-access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions.

OA removes price barriers (subscriptions, licensing fees, pay-per-view fees) and permission barriers (most copyright and licensing restrictions). The PLoS shorthand definition 
"free availability and unrestricted use"— succinctly captures both elements"
There is some flexibility about which permission barriers to remove. For example, some OA providers permit commercial re-use and some do not. Some permit derivative works and  some do not. But all of the major public definitions of OA agree that merely removing price barriers, or limiting permissible uses to "fair use" ("fair dealing" in the UK), is not enough.