It's a large turnip... slightly sweet... cooked it has the constiancy sort of like a potato...
It's a staple in our house... we're having it tonight! with potatos & club steaks...

see this:
http://en.wikipedia.org/wiki/Rutabaga

we usually just boil it until tender, mash in a collander to drain the excess water... then add a little honey & cinnamon...
it's even better if you also add one mashed sweet potato to it...