slipknot
A knot that tightens or loosens easily by pulling.
A slipknot is a type of knot that can slide along the rope it's tied in and can be easily loosened by pulling on one end. The loop gets bigger or smaller as you pull the rope through it, which makes it incredibly useful. If you've ever adjusted a drawstring on a hoodie or a pair of sweatpants, you've used a slipknot: pull one string and the loop tightens, pull the other and it loosens right up.
Sailors, cowboys, and climbers all rely on slipknots because they're quick to tie and quick to undo. A cowboy might use a slipknot when temporarily tying a horse to a post, since one quick pull releases the rope completely. Campers use slipknots to secure tents or tarps, knowing they can adjust the tension easily or untie everything in seconds when it's time to pack up.
The clever thing about a slipknot is that it holds firmly under tension but releases quickly when you need it to. This makes it different from knots designed to stay tight no matter what, like the ones sailors use to secure ships to docks. Sometimes you need a knot that won't budge, and sometimes you need one that gives you flexibility: that's when you reach for a slipknot.