(local (DEFINITION ...) EXPRESSION)The local expression is used to group together related definitions. Each definition in the local is evaluated in order, and finally the body expression is evaluated. Only the expressions within the local (including the right-hand-sides of the definitions and the body) may refer to the names defined by the local. If a name defined in the local is the same as a top-level binding, the inner one "shadows" the outer one. That is, inside the local, any references to that name refer to the inner one.
Since local is an expression and may occur anywhere an expression may occur, it introduces the notion of lexical scope. Expressions within the local may "escape" the scope of the local, but these expressions may still refer to the bindings established by the local.