Compression bathroom faucets have washers or seals that close against a valve seat to restrict water flow through the faucet body. This control is turned off when you turn the handle off. The other three types don't use washers for the off-and-on action, though they do have O-rings and neoprene seals to prevent leaking. They're referred to as "washerless." Because washers and seals wear out with use-resulting in the familiar drip, drip-washerless faucets are generally favored.