Garlic routing is an improved variant of onion routing that encrypts multiple messages together to make it more difficult for attackers to perform traffic analysis and to increase the speed of data transfer.
Michael J. Freedman defined "garlic routing" as an extension of onion routing, in which multiple messages are bundled together. He called each message a "bulb", whereas I2P calls them "garlic cloves". All messages, each with its own delivery instructions, are exposed at the endpoint. This allows the efficient bundling of an onion routing "reply block" with the original message.
Garlic routing is one of the key factors that distinguishes I2P from Tor and other privacy or encryption networks. The name comes from the garlic plant, whose structure this protocol resembles. "Garlic routing" was first coined by Michael J. Freedman in Roger Dingledine's Free Haven Master's thesis Section 8.1.1 (June 2000), as derived from Onion Routing. However garlic routing implementation in I2P differs from the design proposed by Freedman. The key difference is that garlic routing has unidirectional tunnels. Conversely, mainstream alternatives like Tor and Mixmaster use bidirectional tunnels.
List of P2P applications that use garlic routing
I2P - an anonymizing overlay network which allows applications to run on top of it (open source, written in Java)