look up any word, like tribbing:
Mouth Words are an orginal word or phrase you came up.

Warning!!!! Most mouth words will be stolen and tried to be pawned off as original work feel free to bitch smack the person that was stealing your mouth words.
Mouth Words are Pretty much every slang word
by BigE1310 August 24, 2009
A mouth word is a word that when read aloud, can easily be mistaken for another word, or can be spelled incorrectly but when read aloud sounds correct.
A couple examples of a mouth word:

This sentence makes no cents.

Their arr still moar cookies.
by Decisions May 29, 2011