A type of freshwater Cray fish. Smaller than what you would normally think of a cray fish but the tails are very tasty.

http://en.wikipedia.org/wiki/Common_yabby

Some other information
http://en.wikipedia.org/wiki/Yabby

Explains the difference between all the different one's in the world.

http://en.wikipedia.org/wiki/Freshwater_yabby