URL - Uniform Resource Locator
  URN - Uniform Resource Name
  URI - Uniform Resource Identifier

URI is too generic, "I" in URI means "Identifier", which can be either a semantic/natural or a technical/surrogate key. And in many case it's the same Locator is in URL.

IPFS is a CAS (Content Addressable Storage), so an "Identifier" there is a semantic key (i.e. hash of the content).