They’re pretty similar, but there is a slight difference.
Cookie sheets are designed to allow air flow among the cookies to ensure even baking. They are typically flat with open sides (unlike baking pans), to make sliding the cookies off with a spatula just a bit easier.
Sometimes cookie sheets – like this one below – have one or two sides rolled up so you have something to grip when pulling it out of the oven.
A jelly roll pan, on the other hand, has sides that are 1 inch high. These edges prevent the spongecake (used to make jelly rolls) from sliding off the pan as it is placed into, or removed from, the oven. Also, cookie sheets can vary in size but jelly roll pans are supposed to measure 15 1/2 by 10 1/2 inches.