Wikipedia
DD-WRT is a Linux-based firmware for wireless routers and access points. Originally designed for the Linksys WRT54G series, it now runs on a wide variety of models. DD-WRT is one of a handful of third-party firmware projects, which are designed to replace manufactures' original firmware with custom firmware offering additional features or functionality.
The firmware project's name, DD-WRT, was taken in part from the Linksys WRT54G model router, a home router popular in 2002–2004. "DD" are the German license-plate letters for all cars from Dresden, where the BrainSlayers development team lived. "WRT", also used by the OpenWrt router firmware project, is coming to be a generic abbreviation for "Wireless RouTer", which may have been the original Linksys meaning.
Buffalo Technology and other companies have shipped routers with factory-installed, customized versions of DD-WRT. In January 2016, Linksys also started to offer DD-WRT firmware for their routers.