The qth locator app uses your mobile devices location services to calculate and display the six-digit maidenhead grid locator (or simply "locator" as it is commonly referred to) plus additional location information that you can select in the preferences.

The locator is used by amateur radio stations worldwide to indicate the approximative position of their radio station on a grid of 5' longitude and 2.5' latitude.

(Image detail from a picture by Oona Räisänen, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=2528974)