Did you know that fat has nothing to do with weight? That someone who is fit is not necessarily bursting with health? Or that flava is a musical, not a culinary taste? If so, you are at the cutting edge of cool.
Teachers hoping to confound pupils by deciphering street-speak now have a solution. The Longman Dictionary of Contemporary English, published this week, provides a guide to today's English. Entries include "fat" (great), "fit" (attractive), "flava" (Caribbean-influenced music) and, indeed, "yoof" itself.
The dictionary also clarifies the techno-language of cyberspace, for those not as "computerate" (computer literate) as they should be.
Other entries illustrate the concerns of contemporary society. "Mallrats", teenagers who hang around shopping precincts might not worry about the consequences of taking "skag" (heroin), because they think they will "respawn" (return to life after being killed, like computer-game characters).
Della Summers, director of Longman dictionaries, believes that the publication will provide a useful phrasebook for would-be trendy teachers.
"Slang is a way of keeping people out, so only the in-group understand the latest meaning."
Young people will always develop new terms to exclude their elders, she said: "We can't guarantee the words will have the same meaning in two years. It's a snapshot of the language at the moment."
Professor David Crystal, adviser to Longman, said the role of the dictionary is to help where intuitions fail. "There is nothing intrinsically wrong with using informal English, as long as the context is right," he said. "It's precisely the latest, cutting-edge words that people are most uncertain how to use."
Some educationists fear that the dictionary will merely increase the use of slang in essays. Nick Seaton, chair of the Campaign for Real Education, fears that phrases such as "Shakespeare is bootilicious" could be validated by a dictionary entry.
"If teachers or parents don't understand the terms, they've only got to ask. That encourages communication between the generations," he said.