What does 'ten of six' mean in regard to time?

In England we would say ' 10 to 6 ' Or ' 10 past 6 ' .

This would mean

'10 to 6' ; Ten minutes to the hour of six o'clock '.

'10 past 6' ; Ten minutes past the hour of six o'clock '.

You would not hear '10 of 6 ' in England.