I think sex is sex, be it involve the mouth, P/V, or booty. First, all have sex in the name...to hit on the most obvious. Second, and more based on perception than anything else, sex for many is rooted in an intimate encounter - with a casual partner or someone more special. If you're sharing your sexuality with a living being physically it's sex in my book. I think though many will have different views on it, and it doesn't really matter to me. As long as you and your partner share a similar view, chances are your sex like will be rewarding.