Is this classed as subletting?

Hi,

I continue to pay the rent on 2 bed apartment as have required references to prove I can pay the full rental amount

A friend moves into his room a few months down the line. He gives me half share for the time he is in.

To me this does sound like subletting but what if my friend stays for free or only pays towards bills?

Please help.

I didn't find the right solution from the Internet.

References:

Thanks