Why A grid locator is the Maidenhead system's shorthand for where you are on the globe. It encodes latitude and longitude into a short string of letters and numbers, such as FN31 or EM79, with each four-character square covering 1 degree of latitude by 2 degrees of longitude. Hams exchange grid squares in VHF/UHF contests and for satellite and microwave work because they make distance and beam headings easy to compute.
Watch out The idea of a designator for azimuth and elevation describes antenna pointing angles, not a location on the Earth's surface; the two choices calling it an instrument confuse a location code with a piece of test gear.
Grid locator = your spot on the map, Maidenhead style: two letters, two digits, like FN31.