A flatus expelled while fecal matter is sitting in the rectum, therefore forcing the gas around the solid matter and taking some particles along with it as it is expelled through the anus.
A flatus expelled through the anus that is forced around something blocking the anal orifice usually hard packed excrement or a large turd. the effect is a particular smelling flatus whose odor is very similar to whatever is about to be excreted within minutes.
Dude1: "What's wrong?"
Dude2: "I Have to take a crap"
Dude1: "So go!"
Dude1: "Smells like shit, did you just crap your pants???"
Dude2: "Naaa, total Bypass Fart hahah"
Dude1: "Gross, it literally smells like a turd!"
Dude2: "I know, I'll be right back I'm going to take a dump."