Fatty describes something that contains a lot of fat. When you bite into a piece of bacon and notice the white, greasy parts, those are the fatty sections. A fatty cut of meat, like a well-marbled steak, has streaks of fat running through it that make it juicy and flavorful when cooked.

In science class, you might learn about fatty acids, which are molecules that make up fats in our bodies and in food. Your body needs some fat to work properly: it cushions your organs, keeps you warm, and helps you absorb certain vitamins.

The word can also describe foods that are greasy or oily. A fatty french fry might leave your fingers slick with oil. Some fish, like salmon, are naturally fatty in a healthy way, while other foods become fatty from how they're cooked, like fried chicken.

Fatty can also be a noun, meaning a fatty substance or a fatty part of something.

People sometimes use fatty as an unkind nickname for someone who is overweight, but this is hurtful and disrespectful. When discussing food or biology, fatty is simply a descriptive term about fat content, nothing more.