A small release of gas from the anus, but of a smaller quantity than that of a regular fart. One can release a series of fartlets and achieve the same rank effect as a whole fart.
Justin: "I just let out a bunch of fartlets when I was walking past that guy"
A small fart that follows one or more long farts, usually making a noise that is not that different from a tin whistle.
Dave-"Dude! did you just fartlet?