Website / Urban Dictionary
"Urban Dictionary is the slang dictionary you wrote. Define your world"
— Urban Dictionary

"A place formerly used to find out about slang, and now a place that teens with no life use as a burn book to whine about celebrities, their friends, etc., let out their sexual frustrations, show off their racist/sexist/homophobic/anti-(insert religion here) opinions, troll, and babble about things they know nothing about."
— Urban Dictionary's main definition of itself.

Created in 1999 by a college student named Aaron Peckham, the Urban Dictionary combines "anyone can add information" with a dictionary. It has currently recorded over four million words and phrases, mostly slang or slang usage. New words, definitions, and examples are submitted and then approved by the votes of both users and visitors. After that, the new additions are displayed for the world to see, forever.

Many of the terms defined are derogatory or describe sexual acts, so The Urban Dictionary is not exactly something a child should browse through unsupervised. It also gives personal opinions by contributors on certain subjects (bands, movies, books...), with contributors rarely considering the opinions of others. It can be useful for finding out how an unknown term is used, but don't trust it blindly; a significant fraction of the definitions are made up by the person contributing them.

Urban Dictionary offers a Word of the Day on its mainpage. For a long time, they allowed users to rate from the mainpage, resulting in large numbers of negative votes. This option was eventually disabled, largely preventing this.

Urban Dictionary can be found here.