Definition:Transposition

Definition
Let $S$ be a set.

A transposition on $S$ is a $2$-cycle.

That is, a transposition is a permutation $\rho$ on $S$ which exchanges, or transposes, exactly two elements of $S$.

Thus if $\rho$ is a transposition which transposes two elements $r, s \in S$, it follows from the definition of fixed elements that:
 * $\Fix \rho = S \setminus \set {r, s}$

Also known as
A transposition is colloquially known as a two-letter swap.