trichotomy
Division or separation into three groups or pieces.
countable, uncountable
the property of an order relation whereby, given an ordered pair of elements (of a given algebraic structure), exactly one of these is true: the first element is 'less than' the second one, the second is 'less than' the first, or the two elements are equal.
countable, uncountable
[A linear order] obeys the following trichotomy law[.]
Where it comes from
From Ancient Greek τριχοτομία (trikhotomía), from τρίχα (tríkha) + τόμος (tómos) + -ία (-ía).
Adapted from the Wiktionary entry trichotomy (CC BY-SA 4.0).