Varnish Cache is a web application accelerator also known as a caching HTTP reverse proxy. You install it in front of any server that speaks HTTP and you can configure it to cache the contents. Varnish Cache is really, really fast and usually speeds of delivery with a factor of 10x - 50x, depending on your architure.
Varnish is free software licensed under a two-clause BSD licence, also known as the FreeBSD licence. The project was initiated in 2005. Varnish Cache 1.0 was released in september 2006.
The name Varnish comes from when the instigator of Varnish spent a long time staring at an art-poster with the word “Vernisage” and ended up checking it in a dictionary, which gives the following three meanings of the word: