Hashing is a fun form of non-competitive cross-country running with the main objective of working up a decent thirst. Great emphasis is placed on the social aspects - particularly the refreshment session at the aprés-hash. It's a fun activity and must not be taken at all seriously.
If you have hashed before you will know the format, but for the innocent here's a quick rundown on what might happen.
The Hash generally meets at a pub chosen by the hares (those that have set the trail) and the hounds, or pack, and set off at the appointed hour along a clearly defined trail (blobs of flour) with the front runners calling "ON, ON" for the benefit of the slower runners and latecomers catching up.
Every 500 metres or so the trail will end, signified by a check mark which may be in the form of a circle or square. The frontrunners on reaching the check start searching for the new trail.. This can be in any direction, along paths, streets, up rivers and streams or up the side of a convinient hill.
The time taken by the frontrunners to find the new trail allows the runners at the back to catch up thus increasing the chances of everyone reaching the the pub at the end at roughly the same time. The frontrunners will usually find that the cunning hares have laid some false trails in addition to the the real trail - which are designed to ensure that the really fit types, sometimes known as FRBs (Front Running Bastards) will become exhausted more quickly keep together with the slower hashers.
Another device used by Hares to achieve the same objective is the loop whereby the trail might go round 3 sides of a field allowing the back markers to run across the fourth.
Hash runs are usually 4 - 7 miles long and are designed to last 1 - 1½ hours. Revelries in the pub after the run are up to the individual but it has been known for some muddy sweaty hashers to be turned out of the pub at closing time...