Git uses hashes for names

Git uses a hashing algorithm called SHA1 ("Secure hash Algorithm")

Whenever Git saves a piece of information, say a file:

It calculates the file's hash

It stores the file under that hash

The hash becomes the file's name

All references to that file are made using the hash

Git never says "give me file stat.h"

It says "give me file 5b5beb89ba449a9271b3c34d44b529d2a2633235"