A brownie or chocolate brownie is an American invented dessert or snack food: a semi-flat square or bar, made with chocolate or cocoa powder and baked in a sheet pan, something like a dense chocolate cake.
Brownies are common lunchbox fare, typically eaten out of hand, and often accompanied by milk or coffee. They are sometimes served warm with ice cream (à la mode) or topped with whipped cream, especially in restaurants.
A similar bar made with brown sugar and no cocoa is called a blondie. They are also baked in a pan in the oven similar to how traditional brownies are baked.