What does a jelly roll pan look like?

A jelly roll pan is a sheet pan with raised edges of about 2/3 inch. Sponge cake batter is poured onto it and baked, when done it is turned out onto a floured linen dishtowel and a jelly filling spread over the cake. Using the dishtowel for help the cake is rolled up around the filling. The resulting "log" of a cake is sprinkled with powdered sugar and sliced into 1 inch sections for serving.

Unlike a jelly roll pan, a cookie sheet is normally totally flat with no edges.