Concept shop

According to one account, Susan Foreman's mother and father owned a concept shop on Gallifrey while Susan was an infant — although this was only one of multiple coexisting pasts for Susan, alongside her being "Lady Larn" or the Other's granddaughter. The shop sold "philosophical, religious and metaphysical concepts". (PROSE:  A Rough Guide)

Behind the scenes
Prior to getting a nod in Gallifrey: A Rough Guide, the idea that Susan's parents owned a concept shop originated in the BBC radio play Whatever Happened to Susan Foreman?, which is not considered a valid source by this Wiki.