The interest in "social sustainability" has recently increased in the field of urban development. We want societies, cities, and neighborhoods to be economically and environmentally sustainable, but we also want urban areas that are safe, diverse, walkable, and relaxing, just to mention a few examples. Strikingly, however, there is no consensus regarding what definition of "social sustainability" should be employed. Additionally, some people are skeptical about the prospect of finding a useful definition at all and claim it is impossible to satisfactorily define the concept for various reasons, such as its complexity. A potential first step towards navigating this conceptual maze is to provide desiderata for a definition of social sustainability. We defend a list of nine desiderata and thereby create a theoretical framework for analyzing and constructing a definition of "social sustainability". We also examine the skeptical arguments and find that it is premature to conclude that the goal of finding a useful definition is hopeless. With the criteria in place, the future debate can proceed by assessing definitions of "social sustainability" in a more structured and transparent manner. This activity is of upmost importance if we want to create just cities.