Stephenson 2-18 (St2-18, also known as Stephenson 2-DFK 1 and RSGC2-18) is a red supergiant (RSG) star. It is located in close proximity and a possible member of the open cluster Stephenson 2. It is approximately 6,000 parsecs (20,000 ly) away from Earth in the constellation of Scutum and it is one of the largest known stars.