Liquid Democracy is a combination of Direct Democracy, and Representative Democracy. It aims to create a more flexible and fluid way for people to express their Democratic Preference.
Also known as Delegative Democracy, it is a form of democracy where the individual has far more options and control over their democratic Representatives.
The ability to delegate votes to someone you trust, or to vote directly when motivated is one aspect of a Liquid Democracy system. Others include the ability to create Fluid Groups, the ability to participate in Rich Interactive Debate, and the ability to delegate votes to constituted entities defined using Liquid Law.
YOUTUBE fg0_Vhldz-8 A simple introduction to the core ideas of Liquid Democracy.
The term Delegates is preferred to signify the idea that the role of the representative is to deliver the communities decision directly to parliament - wikipedia 
.
History of Liquid Democracy
The internal policies of the Paris Commune are seen as the real-world precursor to the more formalized notions of modern delegative democracy.
Early Soviets, before a Bolshevik majority was reached. Delegative Democracy was gradually eroded in favour of more representational forms of governance. The Unknown Revolution By Voline .
The Industrial Workers of the World labour union uses multiple levels of democracy, including Delegative Democracy.
The first example of Liquid Democracy using a software solution in a real political setting was the local political party Demoex in a suburb of Stockholm called Vallentuna - demoex.net .
Parties Using Liquid Democracy
Pirate Party in Germany, Italy, Austria, Norway, France and the Netherlands use Delegative Democracy with the open source software LiquidFeedback, while in Belgium members of the Pirate Party have developed their own solution called Get Opinionated .
In Spain, "Partido de Internet" developed its own software platform for voting, now an independent free software and commercial project called Agora Voting .