A shortened version of
long neck bottle of beer commonly used in Australia. Depending on which part of the country you are in, it could refer to a 375ml bottle with a longer neck than a
stubby, or a 750ml bottle, the latter being more common.
The 750ml variety are popular among people who like getting pissed and don't mind their beer getting warm, as on long neck is often cheaper than two stubbies, providing more booze for your buck.
The 375ml variety are popular among drinkers of more expensive beers. This is becuase beer producers think that a long necked stubby is more attractive to pretentious wankers than a regular VB style stubby, although in the case of Coopers' Sparkling Ale, I don't give a shit what it comes in. I just like strong beer.
Also a neck that is long, as in "He/She just goes to show you don't need to have a long neck to be a goose."