the epiglottis is elastic cartilage tissue that is coated in a mucous membrane that flaps over and covers the larynx in the back of the throat. More simply, it is the hangy ball in the back of your throat.
Its function is to cover the trachea when swallowing to prevent food/liquids from entering the path that leads to lungs and keep it on its path down the esophagus into the digestive tract.