The Free On-line Dictionary of Computing (30 December 2018):

least upper bound
lub
supremum

    (lub or "join", "supremum") The least upper bound of
   two elements a and b is an upper bound c such that a <= c and
   b <= c and if there is any other upper bound c' then c <= c'.
   The least upper bound of a set S is the smallest b such that
   for all s in S, s <= b.  The lub of mutually comparable
   elements is their maximum but in the presence of incomparable
   elements, if the lub exists, it will be some other element
   greater than all of them.

   Lub is the dual to greatest lower bound.

   (In LaTeX, "<=" is written as \sqsubseteq, the lub of two
   elements a and b is written a \sqcup b, and the lub of set S
   is written as \bigsqcup S).

   (1995-02-03)