Verlan is a form of French slang that consists of playing around with syllables, kind of along the same lines as pig Latin. Unlike pig Latin, however, verlan is actively spoken in France - many verlan words have become so commonplace that they are used in everyday French.
To "verlan" a word, simply separate it into syllables, reverse them, and put the word back together. In order to maintain the correct pronunciation, the verlaned word often undergoes some spelling adjustments. Unnecessary letters are dropped, while other letters are added to make pronunciation logical. There are no real rules for this; it's just something to be aware of. Note that not every word can or should be verlaned; verlan is used essentially to emphasize or hide the meaning of the main word(s) in a sentence.
Let's start with the word l'envers, which means "the reverse." Separate l'envers into its two syllables l'en and vers. Invert them, put them together into a single word, and then adjust the spelling:
l'envers... l'en vers... vers l'en... versl'en... verslen... verlen... verlan
Thus, you can see that verlan is l'envers pronounced à l'envers ("reverse" pronounced in reverse).
Let's try another example:
pourri... pou rri... rri pou... rripou... ripou
Most single-syllable words are just pronounced backwards.
fou > ouf
cool (from English) > looc
The above examples are pretty simple, but verlan gets more complicated when it comes to the e muet, which is a very important sound in verlan. Words that end in e muet (like femme) and words which end in a pronounced consonant and which usually have an e muet sound tacked onto the end (like flic, which is usually pronounced "flique") retain the sound of the e muet when they are verlaned. In addition, when the syllables are reversed, the resulting final vowel sound is sometimes dropped.
flic... fli keu... keu fli... keufli... keuf
femme... fa meu... meu fa... meufa... meuf
arabe... a ra beu... beu ra a... beura... beur
Verlan was invented as a secret language, a way for people (notably youths, drug users, and criminals) to communicate freely in front of authority figures (parents, police). Because much of verlan has become incorporated into French, verlan continues to evolve - sometimes words are "re-verlaned." Beur, commonly heard in the 1980's, has been reversed again to reub. Keuf has been re-verlaned to feuk, with a bonus - it now resembles a vulgar word in English.
Page 2: Essential Verlan