A tart is a shallow pastry case with a filling of food, especially sweet food.

If something such as fruit is tart, it has a sharp taste.

A tart remark or way of speaking is sharp and unpleasant, often in a way that is rather cruel.

If someone refers to a woman or girl as a tart, they are criticizing her because they think she is sexually immoral or dresses in a way that makes her look sexually immoral.