A coping saw is a tool with a long skinny blade that goes up and down, like a seesaw. It has a handle on top and you hold it with one or two hands. You usually use it to cut things like wood or plastic into different shapes.
You put one end of the blade on the material you want to cut, then move the saw back and forth with your hand to make a cut. It's important to be careful when using a coping saw so you don't hurt yourself. But with practice, it can be a really useful tool for making things like picture frames or small sculptures.