UK - Fifty pence (50p).
Half a pound Sterling (100 pence).
From pre-decimal currency 'bob' = shilling and 20 shillings made one British pound. Therefore a modern 50p piece ('bit') = 10 Bob.
Oi Steve, have you got a Ten-Bob bit for the pool-table?
Since the shilling was phased out of British currency, "ten bob" has now come to mean ten ponuds, i.e. one bob is one pound, and so on.
"Look at that guy's car! I bet that cost 'im a few bob"