In general it is the last moss of a mossing
duel. A mossing duel is a contest where
two or more
people moss each other to hold the moss, where a moss is anytime a victory or glory moment is thwarted or stolen with no answer.
The term missmoss originates from the sports of football and
basketball. In those sports, a moss refers to a stolen pass, and a missmoss was when the pass was stolen back or again, making the original mosser "miss the moss." The term missmoss was coined for when multiple mosses happen consecutively, and the last moss of the succession being the missmoss, referring to the fact that the last moss caused the previous mosser(s) to "miss the moss" or have their own moss attempt thwarted.
A missmoss can also refer to the mossing duel itself with the
person coming out on
top being the holder of the missmoss. It is also used to refer to when a mosser gets mossed.