To breakwind or fart. (ie. to emit wind from the
anus, squeeze cheese, float an air
biscuit, a bottom burp, flatulate,
etc, etc).
Bloff is a contraction of "Blow off" (which is an English term for farting (not to be confused with the American term "Blow off" which is unrelated).
Sometimes there is not an inoffensive or
child-safe word for flatulence in polite company, this is where bloffing comes in. To say someone is bloffing is far more socially acceptable, and even child friendly. It's especially easy to tell your kid to stop bloffing in a crowded restaurant, for example. Equally, it's not a big issue if your
child shouts out "I did a bloff" in a supermarket or such!