What does gnu gcc belongs to

Question

it is a compiler or an organization

Answer 1

GNU is not really an organization, it is a licence which tells that your code/program is free to use and free to read (the source code)
When you create a directory on GitHub, you can have a GNU licence for it

Answer 2

gnu - organization
gcc - gnu compiler collection

Answer 3

@Baptiste E. Prunier
That's GNU GPL (General Public License)

But you're right, GNU isn't, strictly speaking, an organization.