A snack is a small serving of food between meals. Enjoy a healthy snack such as apples with peanut butter, or indulge in a bag of chips. After a huge breakfast, you might just want a light snack instead of lunch.
You can use snack as a verb too: "After school, I like to snack on fruit and cookies and listen to music." Snack originally meant "snap or bite" in Middle English, usually in the context of a dog's bite. The noun was also used in the 17th century to mean "a portion or share," which led to the now-obsolete phrase "go snacks," meaning "share with someone."