A property of a message passing system in which each part of a message is transmitted independently along the same route and one part can be forwarded to the next node before the following part has been received. The independent parts are normally small, e.g. one 32 bit word. This reduces the latency and the storage requirements on each node when compared with store and forward routing where a node must receive the whole message before it can start to forward it to the next node. It is slightly more complex than store and forward because each node must keep track of the messages which are currently flowing through it.