Yummy means delicious or very pleasing to taste. When you bite into a warm chocolate chip cookie fresh from the oven and it tastes absolutely wonderful, that cookie is yummy. When you take a spoonful of your favorite ice cream and close your eyes because it tastes so good, that's a yummy treat.

The word is informal and enthusiastic, expressing genuine pleasure about food. You might say “yum!” when you smell something delicious cooking, or describe your grandmother's apple pie as yummy. Little kids often use this word when they're learning to talk about food they like, but people of all ages use it when they want to express pure, uncomplicated enjoyment of something tasty.

While yummy works perfectly for casual conversations with friends and family, you'd probably choose a different word, like “delicious” or “excellent,” for more formal situations, like writing a restaurant review for the school newspaper.