Squid is a Unix-based proxy server that caches Internet content closer to a requestor than its original point of origin. Squid supports caching of many different kinds of Web objects, including those accessed through HTTP and FTP. Caching frequently requested Web pages, media files and other content accelerates response time and reduces bandwidth congestion.
A Squid proxy server is generally installed on a separate server than the Web server with the original files. Squid works by tracking object use over the network. Squid will initially act as an intermediary, simply passing the client's request on to the server and saving a copy of the requested object. If the same client or multiple clients request the same object before it expires from Squid's cache, Squid can then immediately serve it, accelerating the download and saving bandwidth.
Internet Service Providers (ISPs) have used Squid proxy servers since the early 1990s to provide faster download speeds and reduce latency, especially for delivering rich media and streaming video. Website operators frequently will put a Squid proxy server as a content accelerator, caching frequently viewed content and easing loads on Web servers. Content delivery networks and media companies employ Squid proxy servers and deploy them throughout their networks to improve the experience of viewers requesting programming, particularly for load balancing and handling traffic spikes for popular content.
Squid is provided as free, open source software and can be used under the GNU General Public License (GPL) of the Free Software Foundation. Squid was originally designed to run on Unix-based systems but can also be run on Windows machines.
Squid was originally an outgrowth from the Harvest Project, an ARPA-funded open source information gathering and storage tool. "Squid" was the code name used to differentiate the project when development in the new direction was initially begun.