A=432Hz
ISNI - International Standard Name Identifier, like an SSN it identifies creators in the global market. Musicians are not required to obtain one to collect royalties. Acquired at: isni.org
IPI - Interested Party Identifier - like an SSN it identifies specifically Composers and Publishers in music royalty collections. Acquired with registration at a PRO; ASCAP, BMI, SESAC
ISWC - International Standard Work Code - like an SSN it identifies specifically the written composition of a song. There can only be one ISWC per written song. Acquired with registration at a PRO; ASCAP, BMI, SESAC
ISRC - International Standard Recording Code - like an SSN it identifies specifically a recorded version of a written song. A studio version, live version, and cover version will all have different ISRCs. Acquired through your distributor through actually releasing the recording to the market.
IPN - International Performer Number - like an SSN it identifies specifically who performed on a recorded song. No need to acquire one in the US but must register with SoundExchange as a performer to collect royalties.