One harrier (the hare) lays a
trail of flour over a course (s)he chooses. The other
harriers (the hounds) try to follow that trail to the
end where they enjoy munchies and beer (or soft
drinks). The typical hash is 3-5 miles over hill and
dale, through suburbs, woods, malls, et al. The hash
isn't a race, there are no prizes to the swift.
Following the trail is the challenge, camaraderie and
beverages are the rewards.
More information (external
link)