Gnutella Web Cache
A Gnutella Web Cache (often referred to as GWC) is a web service that gives computers connecting to G2, gnutella or similar P2P networks IPs to connect to if they do connect for the first time or do not know IPs to connect to for some other reason. This means GWCs (and similar services) are essential for the initial network connection. However, UHCs (on gnutella) and UKHLs (on G2) are more and more taking over the services once performed by GWCs.
How you can help
If you have a dedicated server and can spare some extra bandwidth then please consider running a GWC. People that don't have a dedicated server or are on normal broadband consumer lines should not run a cache from home.