Define handle.

A handle of a string is a substring that matches the right side of a production, and whose reduction to the
nonterminal on the left side of the production represents one step along the reverse of a rightmost derivation. A
handle of a right – sentential form γ is a production A→β and a position of γ where the string β may be found
and replaced by A to produce the previous right-sentential form in a rightmost derivation of γ. That is , if S
=>αAw =>αβw,then A→β in the position following α is a handle of αβw.