In the Hyperledger Indy docs and code I often see reference to a NYM but I cannot find a clear description of what this means including in the official glossary.
What is a NYM and how does this differ from a VERINYM?
DID's are broadly classified as Verinym or Pseudonym.
Creation of a DID that is known to the ledger is know as a Verinym, and the transaction used for creating a Verinym is known as a NYM transacition.
Check the getting started tutorial for more details.