Certain models of Cisco Catalyst as well as other manufacturers support that feature. What this essentially lets you do is stack several switches, usually 24 ports, with a certain type of connection, and the switch operating system will consider all of these individual switches as one switch. Instead of assigning 4 IP addresses and other configurations to four switches, with stacking or clustering, you have one IP address and configuration. It helps simplify management and also lets all of those switches share one uplink (usually Gigabit Ethernet). There may be more benefits, but those are what come at the top of my head.
-Jeremy-
