Gas released between the buttocks cheeks, expelled gently and or forcefully into the surrounding air. There are numerous methods of release, therefore qualifying a "buttfart" an art form medium. Of course, there are those who do not partake in the exiting and age long celebration of human air. Cheers!!!
"Nice, thats one hell of a buttfart Rick, did you enjoy it or was it rather unsettling?", " Rather Tom, I found that particular buttfart, satisfying and rewarding, a true, and excellent buttfart." "Whoo, stinky."