Protocol

A protocol is a sort of computer language that two programs or computers use to communicate with each other.

In order download from another P2P client, your client must \"speak\" the same \"language\" or protocol.

For example, eMule and eDonkey clients can download from each other (even though they are different programs) but KaZaA and WinMX do not share the same protocol and therefore can't share files between them.

So \"MLDonkey supports 4 networks\" means roughly the same as \"MLDonkey supports 4 protocols\".