Is a sub-division of a track that stores data on a disk?

Yes, a sub-division of a track that stores data on a disk is called a "sector." In traditional hard drives and optical discs, tracks are concentric circles on the disk surface, and sectors are the individual segments within those tracks that hold a specific amount of data, typically 512 bytes or 4,096 bytes. Sectors are the smallest unit of storage that the disk can read or write.