Cosmomart was a planet located in or near the Null Zone that was converted into a shopping mall. They also had smaller shops on various planets.
According to the Tenth Doctor, it was the greatest one of its galaxy, with the food hall zone being the size of Africa.
While visiting the abandoned mall with Gabby and Cindy, the Doctor was captured by Sontarans led by commander Sturg. When this timeline of events was negated, the Doctor took both girls shopping, enduring their indulgent purchases. (COMIC: Supremacy of the Cybermen)
There was once a branch of Cosmomart on Trull, and when Iris Wildthyme became a local celebrity, she promoted the chain. (AUDIO: The Iris Wildthyme Appreciation Society)