It’s a licence that gives you permission to watch/record live TV or BBC iPlayer in your property. It is a legal requirement for you to have a TV licence if you watch live TV or BBC iPlayer.

Do we need a licence each, or can we just have one to cover our whole house?

If you live in a shared student house that has a joint tenancy (for example a 6-bed house that you all share), then you only need one TV licence for your home.