TORONTO - Casual sex isn't just called casual sex any more.

A University of Ottawa researcher says young people have their own codes to describe sexual encounters outside of committed relationships.

Jocelyn Wentland, a doctoral student in experimental psychology, looked at the various types of casual-sex relationships among people aged 18 to 27 and how they are termed.

"We now have names to describe these things in ways that wasn't the case say 20, 30 years ago," Wentland said Thursday.

The four most popular terms used by those in the focus groups included "booty call," "friends with benefits" and "one-night stand." The remaining term has a profanity in it, but can be politely translated as "sex" buddy.

All the terms used to describe the encounters have subtle nuances of meaning, said Wentland.

For instance, a booty call is an invitation from someone you already know who wants to meet for impromptu sex, according to the study's authors.

The booty call is made "usually by text and often late at night," said Wentland, adding alcohol may also be involved.

On the other hand, the one-night stand is usually the classic case of two people who meet at a bar and then hook up for the night, she explained.

"Somebody probably sleeps over but they leave right in the morning. There's no breakfast, there's no hanging around."

As for friends with benefits, they are people who were friends before they became sexually involved. Those relationships, Wentland says, are the most complicated.

See Hollywood's modern casual sex films ... story continues below

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• No Strings Attached

  The first of 2011's casual sex flicks, No Strings Attached starred Natalie Portman and Ashton Kutcher as old friends who decide to start having sex. Will they get together in the end? We can't even guess.

• Friends With Benefits

  Next up on the f**k buddy train were Mila Kunis and Justin Timberlake in Friends With Benefits. Was it a coincidence that the two stars of Black Swan would end up making basically the same movie? Perhaps, but if they were handing out Oscars in this genre, Kunis would be the one holding the statue.

• Knocked Up

  Big burly guy meets leggy blond, and guess what? She wants to have sex with him, just like it would happen in real life. Katherine Heigl and Seth Rogan turn a one-night stand into so much more -- and we can't help but admit we sort of love it.

• What's Your Number?

  A woman who's willing to admit she's slept with more than four men? We can get behind that kind of plotline, particularly when it involves Anna Faris and her ridiculous antics.

• Love and Other Drugs

  This movie starring Jake Gyllenhaal and Anne Hathaway supposedly has more to it than some romps in the sack, but you don't get that from this trailer. So we'll just pretend that these two good-looking actors spend most of their time onscreen in bed, without any attachments at all.

• The People I've Slept With

  The lesser-known The People I've Slept With is a bit grungier than the more mainstream Knocked Up, but it follows a similar premise -- have casual sex, get pregnant, feel badly about your sex life. It does, however, seem to follow a more nuanced path.

• Bridesmaids

  Kristen Wiig's Bridesmaids may ostensibly be about the nutty antics of getting married and the women that make it even crazier, but one of the best storylines has to be around Wiig and Jon Hamm's terrible casual sex relationship.

The friends might be part of a group and not want the others to know about their sexual relationship, she said.

How relationships were defined depended on the frequency of sexual contact, how much personal information is shared, and emotional attachment, among other things.

Wentland's study looked at factors such as how the partners knew each other, whether they added each other to Facebook, and if they discussed the ending of the relationship.

Her study showed both males and females know the rules of conduct for each relationship type.

Other terms that were discussed during the study that did not make the top four included: boy toy, fling, fooling around and no strings attached.

Wentland's article, "Taking Casual Sex Not Too Casually: Exploring Definitions of Casual Sexual Relationships" is published in the Canadian Journal of Human Sexuality.