An apron is something you wear over your clothes to protect them from the mess you make while you're cooking. Some aprons tie around your waist, while others cover your entire torso.
Bakers, chefs, and butchers often wear aprons to keep their clothing clean. It was once common for maids, waitresses, and women cooking at home to wear aprons, while today both men and women wear them. You can also use the word apron to describe the area where a plane is stored or refueled, or the part of a theater stage in front of the curtain. The Old French root is naperon, "small table cloth."