An incision is a surgical cut. A doctor uses a scalpel to make an incision in a patient's skin.
An incision usually refers to a cut that's made during surgery, like an abdominal incision made by a surgeon during a gall bladder operation. A decorative or artistic cut can also be called an incision, such as a cut in carved wood or marble. Incision can also describe the power of sharp observation, like the incision of your friend who can always tell when you're upset, even when you try to hide it.