There is some unique terminology used to discuss specific concepts related to open access. Some of this terminology is restricted to discussions of open access to academic research literature, but some other terms are more widely used in "open" content/software/etc communities.
Gold and Green
"Gold open access" refers to materials that are openly available in their original place of publication. This may be achieved through almost any of the publication-based models of open access. "Green open access" refers to materials made openly available somewhere other than the original place of publication, usually via author self-archiving
Gratis and Libre
"Gratis" refers to materials that are available free of -charge-, but not necessarily with any more rights of use or manipulation than traditional, paid-access materials. "Libre" refers to materials that are not only freely accessible, but also free of any limitations on use or manipulation.
In the free and open source software movement, gratis and libre are often distinguished as "free as in beer" vs "free as in speech". Some have also added an alternative way of looking at gratis as, "free as in kittens" - no cost to acquisition, but not without actual ongoing costs.