Note: I learned Liquid from a group called the "Liquid Pop Collective
." Thus, there is an obvious (unavoidable) bias in my explanation of history and technique, though I will try to give the broadest (but useful) perspective possible.
What is Liquid?
In my opinion, central to almost all styles of Liquid is the concept of "flow." It is a physical connectivity established by the coordinated movements of different body parts, creating an illusion of liquid moving. For instance, one of the rudiments of most people's training in liquid is the handwave. To visualize this, put the fingertips of your two hands together and hold them parallel, and imagine them making a wave.
In this sense, all Liquid styles create an illusion of this flow, which can exist between hands, feet, and other body parts. In many of them, the flow imitates physical laws of the natural world.
Nonetheless, there are other styles that lend to a more abstract approach. In my experience, many of these are focused on contortions, and visual symmetry - however, they still create a "flow" of connected movements, which imitates a fluid substance.
Liquid is different from several other dances in the sense that it is somewhat "freestyle." The dance is unified more by concepts than any series of moves. There is no step-here-step-there explanation of how to dance in this style.*
If the above description seems a bit vague... Well, it is. The plurality of styles and definitions out there come from Liquid's scattered history.
What is the history of Liquid?
The origins of Liquid (at least in America) seem to trace back to some time in the mid to late 1980s. Most stories places Liquid in the beginnings of the rave scene. There are alternate stories; however, the continued presence of Liquid in today's electronic music scenes lends validity to the first theory.
Everyone seems to have their own story (or rather, myth) of the origin of Liquid. I speculate that different styles of Liquid have originated at different places in different times; however, I suspect that the majority of "unique" Liquid styles have been transmitted by people passing the dance on between areas.
In any case, there are two major explanations of Liquid's origins, both of which stem from other dances.
The first is that Liquid came from glowsticking in the underground rave scene. The parallels between Liquid and glowsticking are immediate if one examines the common fluid movements shared by the two. Supposedly, this inspired some glowsticker (who this is will vary depending on who you ask) to drop their stick, and start playing with their hands.
A second, equally plausible explanation, comes from a style of dance called Waving, which originated in the funk and hip-hop movements. Certain aspects of Liquid could easily originate from Waving, the history of which seems to trace back to miming, and the dances of other cultures. As the name implies, Waving consists of passing waves of different types through your body** The similarities between Liquid and Waving are mostly obvious. For instance, the handwave existed in Waving long before it did in Liquid. In fact, the two styles are commonly combined in compliment to each other.
* There are specific concepts that can be outlined. Unfortunately, this would be a tedious practice in words.
**Commonly associated with breakdancing, the style actually existed before b-boying did, but its popularity ascended along with the mainstream inception of breakdancing.