(n.) A switch that also performs routing operations. Usually a switch operates at layer 2 (the Data Link layer) of the OSI Reference Model while routers operate at layer 3 (the Network layer). Routing switches, however, perform many of the layer 3 functions usually reserved for routers. And because the routing is implemented in hardware rather than software, it is faster. The downside of routing switches is that they are not as powerful or as flexible as full-fledged routers.
Because they perform some layer 3 functions, routing switches are sometimes called layer-3 switches. See a breakdown of the seven OSI layers in the Quick Reference section of Webopedia.