Library music (and often called ‘Production Music’) is music written for use for professionals in the video side of the industry. For example, things like adverts, TV shows or trailers. It’s not written specifically for something, other than a themed album on a Library Publisher’s catalogue.
https://www.youtube.com/watch?v=-2CgmA0-X-U
How to compose library music
https://www.youtube.com/watch?v=pZuXQ0CIISA
A collection of library music from YouTube.
https://youtube.com/playlist?list=PL56brqXE7-VM_xWEwkS08Yh6GX6KM1soT
https://youtube.com/playlist?list=PLUXl043M6v4NxohFiElWT4KUUOHc84PEk