Potlatch means "gift" in the Chinook language of northwestern north america. The word itself, and the custom it signifies, was and is used throughout the native societies of the region from california to alaska and east as far as the rockie mountains. A potlatch is a social event in which one group bestows gifts upon another in a lavish ceremony designed to enhance the reputation of the host. The "guests" of a potlatch, recipients of these gifts, are thereby obligated to reciprocate - not immediately, but at the next appropriate occasion (birth, wedding, etc.) Broadly speaking, the potlatch is a social and economic system in which status and rank is established by *being generous*.
It's quite impossible that the english word "potluck" - which dates from well before (1592 earliest citation - in England) contact with the northwest - is derived from "potlatch" - the concepts are related, purely by coincidence.
The term is mentioned in Eric Raymond's "The Cathedral and the Bazaar" in the context of the system of "reward" that may be said to drive the desire to create kick-ass software and give it away: the respect of one's peers. Free software is without doubt a reputation economy in which individuals' reputations are proportional to the value of the the *gifts they have given us*.
Potlatch was also the title of a journal published in the early 1950s by the french post-surrealist group L'International Lettrist, dedicated to the overthrow of western civilization and its replacement with endless festival. The use of this term by european intellectuals at the time was probably due to the influence of the anthropologist Marcel Mauss. The concept passed by this route into the discourse of numerous radicals of the 60s and 70s, most prominently that of the Situationist International whose journal and other writings were all published with the explicit inscription, "no copyright - no rights reserved."
potlatch.net is a website devoted to covering Gift Economy issues (see Gift Economy Data). They also use a wiki (MoinMoin). There are two integrated weblogs, the Potlatch:LoveBlog covering the good news, and Potlatch:FearBlog the bad news.