What is a catalyst reject

Question

I failed the E check due to a catalyst reject but i have no idea what this is. I don't know if it is a sensor or something internal within the engine. Is this a part that i can purchase from autozone or any auto part store?

Answer 1

try to use a different obd-II reader, thats not a correct code

Comments

This is what the machine said, I'm not for sure of the code but when my suv was on the machine it read catalyst reject.