Confluence is a property of rewriting systems (such as evaluation in the lambda calculus and associated extensions). It states that, if there are two different ways to rewrite an expression, then there is a way of continuing to rewrite each intermediate result to arrive at the same final result. So the two rewriting paths may diverge, but they can be made to come back together. This property allows one to show that a normal form (one that cannot be reduced further) is unique.

This is not so important for Racket since Racket’s rewriting system is deterministic. There is at most one way to rewrite any given expression.