Open Water Diver...is the training everyone gets that covers basic assistance - like sharing air, removing/replacing gear in the water, breathing from a free-flowing regulator, emergency ascents, and a shared-air ascent.
Rescue Diver (AKA Stress & Rescue) is a course that expands on fundamentals learned in Open Water and Advanced Open Water to cover managing a panicked/stressed diver, enacting an emergency action plan, searching for and recovering a lost diver, as well as emergency first aid. I teach it, and it’s available at most dive centers.