A cookie is a round, sweet baked good that's often eaten with a glass of milk. You might bake three dozen cookies to sell at your swim team's bake sale.
In Britain, it's a biscuit, and in the US it's a cookie. In both cases, it's a small cake that's baked on a cookie sheet. Your favorite cookies might be chocolate chip — or maybe you're more of an oatmeal raisin cookie type. When you see cookie in the context of computers, it means a bit of data that's sent from a website to your browser. This type of cookie helps your computer remember passwords and web pages it's visited.