What is Open Access? Open-access is digital, online, free of charge, and free of most copyright and licensing restrictions.
"Scholarly communication is the system through which research and other scholarly writings are created, evaluated for quality, disseminated to the scholarly community, and preserved for future use. The system includes both formal means of communication, such as publication in peer-reviewed journals, and informal channels, such as electronic listservs."
More on "Scholarly Communication in Crisis" (source: Association of College & Research Libraries)
The following categories describe several different types of open access publishing models:
This short video by Nick Shockey (of SPARC),Jonathan Eisen (professor at UC Davis) and Jorge Cham (of PhD Comics) gives an overview of the history of scholarly publishing.