A superblock of VFS (and ext2) is a block (one or more contiguous sectors) that describes the file system as a whole. A file system may contain one or more superblocks. However, block 0 (the first block) must be a superblock. Other superblocks, identified by a “magic number”, can be distributed to the rest of a file system as backup superblocks, just in case block 0 gets corrupted.
The superblock contains the block number to the first inode of the entire file system. The first inode of represents the root of the file system.