Serrations are the small, sharp bumps on the edge of a knife or a saw.
Serrations are good because they help the knife or saw cut things better.
Examples:
The knife has serrations on the blade.
The saw's serrations make it easier to cut wood.
I like the feeling of the serrations on the knife.
The bread is easy to cut because of the serrations on the knife.
The dinosaur's teeth had serrations like a saw.
The serrations on the saw are like tiny mountains.