Mules are slightly smaller than their horse parent, and when they grow they share traits of both a donkey (the long ears), and the horse (color, tail, etc.). A Mule in the grass.
For example, a 2014 Ford F-150 is considered a half ton truck but most variants can carry a lot more than 1,000 pounds in the bed. Since these terms are probably not going away any time soon, it's best just to think of them as smaller, mediumest, and more than medium.. (Pause for laughter).
These tend to weigh over 6,000 pounds empty, have a payload max of 3,000-4,000 pounds and can tow up to around 13,000 pounds. They're also a lot stiffer than Half-Ton trucks so think long and hard about whether or not you really need the extra capability before you buy one.