An ISWC code is an acronym for International Standard Musical Work Code.
The ISWC is a unique and permanent identifier code assigned to a specific musical work or composition written by the songwriter.
An ISWC can be associated with an infinite number of ISRCs since there can be several recorded versions of a song each with its own unique ISRC, all associated with the same ISWC. For example a remix version, cover, acoustic, etc.