Definition:Composition


 * Set Theory: Composition of Mappings or Relations: $$\mathcal R_2 \circ \mathcal R_1 = \left\{{\left({x, z}\right): x \in S_1, z \in S_3: \exists y \in S_2: \left({x, y}\right) \in \mathcal R_1 \and \left({y, z}\right) \in \mathcal R_2}\right\}$$.
 * Abstract Algebra: Another word for an operation, usually binary.