It’s jargon. There are two layers of cli commands in Git. One - user friendly like “git commit”, that does abstract things like commits, diffs, etc. It is called “porcelain”. Another level is low level commands. They are used by “porcelain” level commands to actually manipulate Git’s database. They allow to create objects, change objects, cause re-packing, manipulate refs (branches and tags but more than just that), manipulate object types and look inside objects.