Usually coffee, but could be any beverage with a browncolor. Typically one uses the term in the context of an unsavory environment such as work, church, or 12-step meetings.
Guy 1: 'Hey man, lets take a break at 4pm and get some browndrank'
Guy 2: 'Ok'
A person who fancies himself an expert in many things but whose expertise derives largely or solely from the internet. The shallowness of his/her knowledge base is often betrayed by obvious factual errors. (The antithesis of "Encyclopedia Brown", the fictional boy detective in the eponymous literary series.)
Jim: Did you know that scientists found vestigial wings in a mummified komodo dragon?