Adapted from The World Hash House Harriers Home Page - http://www.gthhh.com/:
Hashing is a more-social version of the classic game of "hare and hounds," also known as the "paper chase." There are a number of running groups who engage in variations of this non-competitive activity, the most eccentric of which are the Hash House Harriers, or H3 for short. The H3 world directory lists 1947 groups, located in 1266 cities in 185 countries, but there is no requirement for any group to affiliate themselves as part of the H3 mind-hive.
Hashing sets a pack of hounds (runners) to chase down a trail set by one or more hares (other runners). When the trail has been completed, the kennel (as H3 groups are also known) gather together for a social activity known as "On In" with refreshment, humor, song and often the occasional feast, sometimes known as "On After." Most groups welcome young and old, fast or slow, runners or walkers. The only prerequisite for hashing is to have a sense of humor.
Hashing appeals to a variety of persons because there are traditions which vary from kennel to kennel, and most kennels keep what happens there within the confines of the kennel. No two kennels are alike; some are family hashes, others are adult-only groups, and some strictly participate in pub crawls.