Many people only recognize two types of relationships: girlfriend/boyfriend, and just plain friend. But I think that there are in fact many different levels of those two, plus many other kinds of relationships.
First there is just friends, no physical attraction, just like to hang out and talk and do stuff together (not sexual). Pretty shallow, but still close enough to be considered a relationship I think.
Then there's kind of in between-ish. They hang out and do stuff, but there is some physical attraction on both sides. They both want to do sexual stuff, and they do but not that much, maybe just kissing and a little bit more, but it's mostly just friends and hanging out. Like a step above friends.
Then, there's purely sexual. They almost don't hang out, just kind of use each other as fuck buddies, pure pleasure. If both are aware of it and both okay and happy then there's nothing wrong. But a lot of times this can lead to a full-blown boy/girlfriend type relationship as some of the physical attraction sort of turns into emotional bonding. I mean, sex is intimate, you can't argue that. And it's kind of hard for some people to continue to do it with someone they don't really care about all too much.
And lastly, there's the standard, normal relationship relationship. The full-blown relationship where they have true feelings for each other, they connect, they don't just talk and hang out, but they understand each other and care for each other. But a relationship like this must include physical attraction. With close emotional feelings for one another comes the desire for sex, just about in all scenarios. It's basically a blend of all the other kinds mixed in. But it's all that, plus love, that mysterious crazy weird awesome mystical unique emotion that no one really does truly understand... And you can't get love from any other kind of relationship. A lot of people say it's worth the extra work for a relationship, just to get that love. Everyone needs a little of that love sometime or another
So some people may argue over which kind of relationship is best, some may say it just depends. These are pretty much general examples of types of relationships, in my opinion. Have fun...