A binary operator representing multiset union or the join operation in lattice theory and set theory.
Examples
Binary join operation in lattice theory
a \Cup b = \sup\{a, b\}
Join of multiple elements in a lattice
x_1 \Cup x_2 \Cup x_3 \Cup x_4
Join operation with a set expression
A \Cup (B \cap C) = \sup\{A, B \cap C\}