A listing is a predetermined list of severe disabilities, that if you meet, equal, or exceed (are as bad as, equivalent to, or worse than) the severity of the listed disability, then you will be found disabled.  They are a part of element 3 of the 5-step sequential process (5 elements of disability).  So, the goal is to have medical equivalency to a listing, so that you can get a check every month, and medical insurance.  Almost all listings require you to meet severe disability levels; however, due to more recent statute changes, now some require extreme disability levels.