Note, this is an advanced configuration feature. Most deployments can rely on the <Logout> shorthand element.
The <md:SingleLogoutService> element is used to configure handlers that are responsible for processing logout protocol messages from an IdP. These are protocol specific, but generally fall into two classes: requests, which tell the SP to perform a logout, and responses, which conclude a logout event initiated by the SP.
As a multi-protocol system, the SP itself is oblivious to specific logout protocols; each handler provides the implementation of a particular logout protocol.
Handler implementations exist for these protocols. Precisely which handler is defined the the Binding attribute.