A binary operator representing disjoint union of sets or categorical coproducts in algebra and topology.
Examples
Disjoint union of sets
A \sqcup B \sqcup C = \{1,2\} \sqcup \{3,4\} \sqcup \{5,6\}
Disjoint union in topology
X = \bigsqcup_{i=1}^n U_i
Direct sum of vector spaces
V = V_1 \sqcup V_2 \sqcup V_3