A fart that is "load-bearing", i.e. when one farts and a little shit comes out, too.
The term originates with the fact that a wall or other construct that is load bearing is sometimes referred to as being structural.
Also known as a "shart" or a "fart surprise".
I thought it would just be a little gas, but God help me, that fart turned out to be structural.
Man, after drinking 3 gallons of beer last night I've had nothing but structural farts today.