Food that is stale, tasteless, foul-smelling and kept overnight, as well as leftovers and anything unfit for offering, is dear to those of tamas.
Explanation
Krishna is finishing his description of three kinds of food, after the passion-driven (rajasic) foods in the previous verse. Here he describes what appeals to people ruled by tamas, the guna (strand of nature) of dullness and inertia: food that is stale, flavorless, rotten, kept overnight, left over from someone else's meal, or ritually impure (amedhya, "unfit for offering"). The word yātayāmam can also mean food cooked long before and gone cold, and traditions vary a little on how strictly to read "leftover" (ucchiṣṭa), but all take the verse as describing tamasic food.