Like a pit stop, except done when driving on the road, too far from your home restroom. Typically happens on road trips, after a night of drinking, or else shortly after eating fast food.
Husband and wife are driving on the highway, the husband swerves the minivan into the rest area...
Wife: What are you doing?! We just ______ (ate, filled up the car with gas, etc.).
Husband: Sorry, gotta make a shit stop!
When one goes to the bathroom to piss, but subsequently decides to take a shit as well. Similar to a pit stop in nascar, if a driver needs to get gas, he/she might decide to change the tires as well while they're at it.
Anonymous kid A: God dude I got out of Math class and had to take a piss the entire fucking class, I felt like I was about to get a UTI but I had to copy this Asian chick who was rocking a Hello Kitty watch so I knew she knew her shit.
Anonymous kid B: Fuck that class dude, math is the lesbian sister of biology, so my conservative catholic parents would never let me take it. How was that piss?
Anonymous kid A: Dude, it started out as a piss, but since I was already there I decided to take a shit stop and Release the Kraken on that toilet!