Basically, a Nash Hash is a "National" Hash where a country or region's Hash chapters get together once a year for a party.  Usually, it is a 3 day weekend held somewhere in the country in question and  hosted by one the local Hash chapters.  Of course it being the Hash, nothing should be considered cast in stone.  (One year the German Nash Hash was held in the Czech Republic!) 

A "rego" (registration fee) is required to reserve your spot at the event.  This money goes for the food, drinks, lodging, and entertainment and sometimes even a T shirt.

Nash Hashes are usually open to everyone and people come from all over the world, but events are held to about 150 Hashers for manageability. 

What to expect:  A place to stay (think Hostel), food and snacks, Friday night pub crawl, Saturday Hash run, Saturday night dinner and party, Sunday hangover run, and of course, lots and lots of beer - not to mention 150 of your closest drinking buddies. 

Think of it as a chance to relive those lost college days.   And, it's a great place to meet old friends and make new ones (and the perfect excuse to get away for a long weekend).