a casual heuristic used to indicate rough estimates in a limited set of categories, usually small, medium, and large, as in: “We can’t do a full bottom-up evaluation of each market segment, just use t-shirt sizing for now”; derived from the practice of standardizing clothing into a limited set of sizes that provide adequate fit options for the majority of the population; related to traffic light (verb), when options are sorted into three categories that represent yes, maybe, and no (or analogous variants thereof)