Gaelic is an adjective that means "pertaining to the Gaels". As a noun, it may refer to the group of languages spoken by the Gaels, or to any one of the languages individually. In particular, the different Celtic languages spoken in both Ireland and Scotland are very often referred to just as "Gaelic", which can cause confusion.
Literature, most generically, is any body of written works. More restrictively, literature writing is considered to be an art form, or any single writing deemed to have artistic or intellectual value, often due to deploying language in ways that differ from ordinary usage.
A beautiful literature springs from the depth and fullness of intellectual and moral life, from an energy of thought and feeling, to which nothing, as we believe, ministers so largely as enlightened religion.
While the guardians of “literary” fiction still give each other prizes and writers can still achieve stardom and create good work, the fact remains that it is a movement that has lost all its creative force as a movement.
Orson Scott Card, Quo Vadis? (Published in Nebula Awards Showcase 2008)
That doesn't matter. Don't you give up on this [library] card. Because books can be solid gold. Yeah, the great ones have gotten us through the nights for centuries. Just give a writer an hour to hook you and if he can't wish him the best of luck and find someone else.