What is Socks4 proxy?

[Groc]

Hello,
What is the socks4 proxy option for?
Thanks

[Neereus]

Some people are behind a firewall (like at work) that blocks port 8333.
If you have access to a proxy using socks4, then you can use that option to bypass the firewall.
This allows the use of the bitcoin client even behind a firewall.

[Sawzall]

Also, the Tor client is a local Socks4 proxy that redirects connections though the Tor network. The Bitcoin client can therefore be configured to use Tor pretty easily.