A binary operator representing tensor products, direct products, or cross products in algebra and vector spaces.
Examples
Tensor product of vector spaces
V \otimes W \text{ is the tensor product of spaces } V \text{ and } W
Direct product of groups
G_1 \otimes G_2 \otimes G_3
Kronecker product of matrices
A \otimes B = \begin{pmatrix} a_{11}B & a_{12}B \\ a_{21}B & a_{22}B \end{pmatrix}