I would like to add to their definition and also define a booty call not as the actual call itself, but the person you are calling. That person becomes your booty call.
So do you have a booty call? Or more than one booty call? (Or are you someone else's booty call?) There are just so many questions! What are your booty call rules? If you even have any rules?
The typical booty call text usually occurs between the hours of 11-3. And usually one or both of you are drunk. Most of the initial texts start like this: "u out?" or "what you up to?" or a simple "come over now." Whatever it is, in the words of Carrie Bradshaw "the subtext of that text is booty." And you both know it. Do you go to his place or does he come to yours? Do you guys talk/hang out at first or just get down to business? Do you spend the night or leave when you are done? Do his friends know about you? Do you actually have feelings for him but take the role of booty call because its better than nothing? Finally, do you two ever hang out sober and in daylight?
The thing that is tricky with the booty call is that is if you haven't DTR'd (defined the relationship) then one person is bound to get hurt. Either one of you will meet someone else and blow off the other or you will get bored with him and move on to a different booty call (perhaps even keeping this person in your rotation "in case of emergency"). And since its just a booty call, you really don't owe them an explanation, do you? I mean it is common courtesy to let them know that you are seeing someone now and shouldn't be bothered. I am sure you would want that courtesy as well. It's the least you two can do for each other.
Do yourself a favor, if you have a booty call, it might be helpful for you two to clear the air right away and make each other aware of what you are doing and set some parameters. It sounds unnecessary for such an arrangement, but you don't want to be the one, at 3 in the morning, drunk and headed home alone and getting no text back. Or maybe you will pass out before you even care. But if you do care, it might be time to re-evaluate why you are doing what you are doing. If its just for fun and literally no strings attached, go for it. More power to you actually! But if you somehow think that this will turn into a relationship, that is doubtful, so set some ground rules and enjoy the ride.