Dosnet (Denial of Service Network) is a type of botnet and mostly used as a term for malicious botnets while benevolent botnets often simply are referred to as botnets. Dosnet's are used for Distributed Denial of Service (DDoS) attacks which can be very powerful.
They range in size from a couple of bots to a couple of thousand bots up to over a hundred thousand bots.
Many dosbots use the IRC protocol, but some use their own protocols.
More advanced dosnets utilize SSL and cryptography to prevent packet sniffing and data inspection.
The botmaster can use the bots to send a data flood to other computers or networks. The botmaster can often also make them fetch a new version and update themselves.