How big is a D&D square in IRL?

Could you elaborate on the dimensions of a Dungeons & Dragons (D&D) square in real-life (IRL) terms? Are you referring to the standard grid size used in the game for mapping and measuring distances? If so, what specific size, if any, does it correspond to in real-world measurements? Additionally, is there any industry standard or convention for converting D&D grid squares into real-world units?