One who is similar to a half-tard but has even less retard blood in their system. They can almost always function normally in society, and only fall prey to their heritage once in a while (usually one time a month). Quarter is to represent 1/4 of retard blood, so in reality they are 3/4 smart. It is the closest possible to being non-tarded that those with retard blood can get. The opposite is a full-tard
Guy 1: "Whoa. Did you hear? Dan got his nipples pierced!"
Guy 2: "Fuck. What a goddamn quarter-tard."
Guy 1: "Aye."