FAT and FAT32 are file systems that are defined as follows:
FAT (File Allocation Table): A file system used by MS-DOS, Windows 3.x, and Windows 95/98. All later Windows operating systems also can use the FAT file system. The operating system maintains a table to keep track of the status of various segments of disk space used for file storage.
FAT32 (File Allocation Table): A derivative of the file allocation table (FAT) file system. FAT32 supports smaller cluster sizes than FAT, thus providing more efficient space allocation on FAT32 drives. FAT32 is designed for larger disks than FAT.
See also NTFS.