When someone says “ratchet” the first thing most people think of is a socket wrench. It uses a ratchet mechanism to be able to turn one direction but not the other.
The term “ratchet” also refers to one of the two working parts of a wire tie. That is what you call the teeth on the flexible leading end (the tape) of a wire tie. If you look at them closely, you’ll see that one side of each tooth is vertical (at a right angle to the tape) and the other side is at an angle. This angle is what lets you easily push the head of the tape through the pawl but prevents it from being pulled back the other way.
When you try to pull it apart, the vertical side of the pawl can’t pass through the ratchet and the wire tie stays locked.
It is a simple (some might even say elegant” design that makes a wire tie invaluable when you need an inexpensive and reliable mechanism for doing things like bundling cables or installing awnings.