No quarter

Where did the phrase "no quarter" come from and what would be the correct usage of the term? I'm guessing it's origin comes from sailing somehow but haven't been able to find a good definition anywhere. Thanks.

The Tatty old OED gives:

Quarter (Mass Noun): pity or mercy shown towards an enemy or opponent who is in one's power: the riot squad gave 'no quarter'.

-ORIGIN Middle English: from Old French quartier, from Latin quartarius 'fourth part of a measure', from quartus 'fourth', from quattuor 'four'.