Origin
In plain terms
The default name for the main remote repository.
Going deeper
'Origin' is the conventional name Git gives the remote you cloned from, used as the default push/pull target. It's the repo's home base.
Under the hood
Just a convention/alias; you can rename it or add others like 'upstream'.
Examples
git push origin, default remote, cloned source, git remote -v.
Think of it like...
Like 'home base' that your local copy reports back to by default.