inode

The record that holds everything about a file except its name: owner, group, mode, timestamps, and where the data blocks are. The name lives in the directory entry that points at the inode. That is why mv notes.txt archive.txt is instant on a 40 GB file: stat -c '%i %n' prints the same inode number before and after, because one directory entry was rewritten and no data moved. It is also why rm removes a name rather than a file — the kernel frees the blocks only once the last name pointing at that inode is gone and no process still holds the file open. Treat the name as the file and both halves surprise you: a rename you expect to take minutes, and a deletion you expect to be reversible.