True, but it would be something a therapist would understand. I think you should use your own words, though. Hooking up is understood, and they may ask you details about your interactions with others or why you have casual sex. And the obvious "duh" reasons is "Because I like it." Haha.

When asked, though, just remember they are not going to judge you off the bat. They did not spend years educating and molding their minds on thinking above the average joe/jane in psychology. If they try to shame or judge you, then get another therapist.