Assets can f.x. be sound, music, gfx, concept art, code, scripts an so on. Somebody might be able to explain better what a license covers. Usually it seems to be the right to market something as being something specific? E.g. somebody owns the D&D IP. A company creates D&D artwork for whatever reason. Said company may own the rights to the artwork, but they can't sell it as D&D artwork without getting the permission from the IP owner (licensing it) to sell it as D&D Artwork. Stuff like that (IP's, Branding, Trademarks etc.) can be messy and involves many lawyers. No idea who holds the rights to sell Icewind Dale games these days, Hasbro?