That'd be a friends-with-benefits relationship, which is actually different from an NSA relationship. Typically, NSA relationships are between two people who don't have much history together, if any. It should be with someone you don't have any personal feelings for, even platonically, and ideally, someone you barely know. The reason for this is because unlike friends-with-benefits relationships, NSA relationships do not have any ties at all to the person you're seeing. Many people fail in their FWB relationships because when you start hooking up with a friend or someone you already know, it's easier to become emotionally involved. It also makes following all the other rules easier if you're entering an NSA relationship with someone you don't know very well. You'll probably only like them for their looks and for the sex, which is really all you need for an NSA relationship. The only reason it has the term "relationship" attached to it is because you'll both become regular sexual partners. It's all about the physical pleasure, and with friends, you'll be more likely to give them more than that, such as emotional support. In this type of relationship, there's no need to worry about that -- all you need from each other is sex and a good time. Have no other expectations.