The term 'SHORTEST OR LONGEST DAY OF THE YEAR' refers to the solstice, which is an astronomical event that occurs twice a year when the Sun reaches its highest or lowest point in the sky. The solstice marks the longest day of the year (summer solstice) and the shortest day of the year (winter solstice). During the summer solstice, the days are longer and the nights are shorter, while during the winter solstice, the days are shorter and the nights are longer.