Ordnance Survey grid is a geographic coordinate system used primarily in UK.
It uses letter prefixes and digit suffixes instead of degrees to refer to areas of UK.
For more information see this
To input a latitude/longitude, first enter the N,S or W,E symbol after which enter the degrees
minutes seconds, separated by space. For example: [W 47 1 32] means 47° 1' and 32" West longitude.