What counts as sex?

Bill Clinton and Monica Lewinsky may have changed today’s college students views on the matter: 

So, does oral sex count as sex?

That’s the question University of Kentucky researchers asked nearly 500 college students in 2007. Only 20 percent of them said oral sex was sex — which is a steep drop from the 40 percent in similar studies in 1991 and 1999-2001.

Changing definition of sex (Washington Post)