But all too often we don't know exactly what we're talking about. What's considered getting to third base these days anyway?
And when it comes to philandering politicians, the line on what's considered sex is especially fuzzy.
President Bill Clinton said oral sex wasn't sex. South Carolina Gov. Mark Sanford says in his latest revelation that he with women other than his wife and Argentine mistress, but "didn't cross the sex line." He wouldn't say what that meant.
If those distinctions have you confused, you aren't alone. Neither are Clinton and Sanford.
Americans just aren't explicit when they talk about having "had sex."
"Sex is a word and nobody is really in charge of that term," said Kinsey Institute scientist Erick Janssen. "In a way, our thinking of sex and definitions of sex is more complex than they were in the past."
In 1998, just as Clinton was defining what "is" is, two other Kinsey researchers were publishing a paper in the prestigious Journal of the American Medical Association on how people see sex. The answer: We can't really agree.
The study, based on 1991 survey of 599 college students, found something odd considering the parsing of male politicians. Women in general were less likely than men to consider oral sex or mutual masturbation as having "had sex."
Of the women, 37 percent considered oral sex as, well, sex. Forty-four percent of men did.
A second survey in 1996, asked "Is oral sex 'real' sex?"
About 52 percent of the men said yes, but only 46 percent of women did.
"These data make it clear that general agreement regarding what constitutes having 'had sex' and how sexual partners counted cannot be taken for granted," researchers Stephanie Sanders and June Reinisch concluded in their paper.
That's a problem, especially in a relationship if two people don't discuss those differences explicitly, Janssen said.
In the classic Meat Loaf song, "Paradise By The Dashboard Light," radio broadcaster Phil Rizzuto describes baseball players advancing bases, as a young couple negotiates intimacy in their car.
It helped cement the public on the 1960s analogy of first, second, third and home to increasingly intimate sexual activities.
But even that is changing. According to a book by Australian sex researchers Juliet Richters and Chris Rissel, in the 1960s third base was "touching below the waist."
"Nowadays it seems that for many people the pattern of accepted activities includes oral sex as third base," Richters and Rissel wrote in "Doing it Down Under."
Janssen said it's difficult and unfair to compare terms now to decades ago because society is so different.
"People tend to not always define just in terms of behavior anymore, also in terms of intentions," Janssen said.
And intentions - lusting in your heart just like former President Jimmy Carter - bring about a whole other issue for politicians, because cheating is so loosely defined, Janssen said.
Is it cheating to go out to dinner with someone other than your spouse and not tell, or what about dancing together? Sanford met his future mistress in Uruguay on the edge of a dance floor.
Sanford himself said, "If you're a married guy at the end of the day you shouldn't be dancing with somebody else."
Americans tend to judge politicians more harshly about marital infidelity than Europeans, said Janssen, who is Dutch. It's a cultural thing.
But we do have something in common with those across the Atlantic, Janssen said.
Europeans don't really have explicit definitions of sex in their languages, either.
So, they can be just as vague when they talk about it as we are.