We did explain DHT in our jargon piece back in 2006 but after 3 years, we decide to cover it again.
The easiest way to think about DHT is to imagine it as a form of ‘super tracker’, in some ways a lot like Win MX and Kazaa of old.
Not really a surprise since the documentation and even the Wikipedia page are filled with technical jargon, and no simple explanation.
Without that basic understanding confusion is inevitable.
The routing table becomes more detailed as IDs get closer to the node's own ID.
Nodes know about many other nodes in the DHT that have IDs that are "close" to their own but have only a handful of contacts with IDs that are very far away from their own.
Notable distributed networks that use DHTs include Bit Torrent's distributed tracker, the Coral Content Distribution Network, the Kad network, the Storm botnet, the Tox instant messenger, Freenet and the Ya Cy search engine.
DHT has been included with many clients since it first debuted in the summer of 2005.
A distributed hash table (DHT) is a class of a decentralized distributed system that provides a lookup service similar to a hash table: (key, value) pairs are stored in a DHT, and any participating node can efficiently retrieve the value associated with a given key.
Responsibility for maintaining the mapping from keys to values is distributed among the nodes, in such a way that a change in the set of participants causes a minimal amount of disruption.
Bit Torrent uses a "distributed sloppy hash table" (DHT) for storing peer contact information for "trackerless" torrents. The protocol is based on Kademila  and is implemented over UDP.
Please note the terminology used in this document to avoid confusion.