The idea of liquid democracy responds to a widely-felt desire to make democracy more "fluid" and continuously participatory. Its central premise is to enable users to employ networked technologies to control and delegate voting power, to approximate the ideal of direct democracy in a scalable fashion that accounts for time and attention limits. There are many potential definitions, meanings, and ways to implement liquid democracy, however, and many distinct purposes to which it might be deployed. This paper develops and explores the "liquid" notion and what it might mean for purposes of enhancing voter choice by spreading voting power, improving proportional representation systems, simplifying or aiding voters in their choice, or scaling direct democracy through specialization. The goal of this paper is to disentangle and further develop some of the many concepts and goals that liquid democracy ideas often embody, to explore their justification with respect to existing democratic traditions such as transferable voting and political parties, and to explore potential risks in liquid democracy systems and ways to address them.