What does "liking back" and "returning likes" mean on instagram?

[Julia]

I see a lot of people do it on celebrity instagram accounts or very popular accounts.... what does it mean?

[A]

They say this basically to promote their account or get more followers. They are saying that if you go on there page & like their pictures they will go to your page and like your pictures.

[Nadia Josephína]

Yea it's just what people say to get more followers. Their saying if you like their pictures they'll like yours. Sometimes they do but on really popular accounts their not very likely to return like since they do have thousands of followers.