A device used on forums and in chatrooms to remove language thought to be unsuitable.
There are a number of ways round the one ARRSE uses, from modified spelling such as cnut and fcuk, to the use of bold text on one character to break the word up and adding a spurious punctuation mark.
It can also be used to swap one word for another, such as "bollocks" to "balls" or "Worthing" to "seaside town" (see Blondebint).
The difficulty comes when you want to use a word like Cumbria, when the filthter spins into overdrive. And then there are words like Scunthorpe, Clitheroe and Spunkchester guaranteed to cause havoc.
Some Filthters actually change words so bizarrely that they have become internet words in themselves. Words like assassination and constitution end up as buttbuttination and consbreastution I kid you not!
More analysis is needed in this new field of cunning linguistics.