An inode is a data structure and it is an entry in inode table. Inodes contain information about the regular file and directory. It is a traditional Unix- style file system such as ext3 or ext4. The inode number is also called as an index number. It contains attributes like files, permissions, UID, GID, File Size, the number of likes, the location of the file on hard disk. To reach a particular file with its “name” needs an inode number corresponding to that file. But to reach an inode number you don’t require the file name. In fact with the inode number, you can get the data
df-i is the command used in Linux to check the number of inodes in a file system.