Varnish is an HTTP accelerator. An HTTP accelerator (often called Reverse Proxy)
is an application that stores (caches) documents that have been requested over
the HTTP protocol.
Based on certain criteria the next client requesting the document is either
given the cached document, or a "fresh" document requested from a backend
server. The purpose of this is to minimize the requests going to the backend
server(s) by serving the same document to potentially many users.
The goal of Varnish is to be a very fast, stable and effective light-weight HTTP
accelerator daemon, by using modern and effective technologies. Ease of
managment and good documentation is also a main goal of the project since the
lack of either one will render Varnish useless.