UDP
From AMule Project FAQ
UDP is similar to TCP and is also a main part in internet's core structure. The main difference with TCP is that it doesn't provide reliability, which makes it perfect for those cases in which we don't really mind as much in verifying that the data gets to its destination as in just trying to send a lot of data.
An example where UDP is vastly used are videoconferencing.
More information about UDP can be found at Wikipedia's UDP article.
