10 pounds of fart being held back by one ounce of crap. The crap comes out jet powered and often creates artwork on the side of the toilet. Named for the 'blap' sound it makes coming out.
It's also artificially created by forcing a crap. Taking a 10 minute crap in 2 minutes often creates a blap crap.
Be right back, gotta go take a blap crap.