The term 'calendar heading' refers to the top row of a calendar, which typically includes the days of the week, the DATE, and the month. The crossword solutions for this term are 'DATE' (4 letters), 'JUNE' (4 letters), 'Mon' (3 letters), and 'MTWTF' (5 letters). The word 'DATE' indicates the numerical day of the month, while 'JUNE' is the name of the month. 'Mon' is an abbreviation for Monday, and 'MTWTF' stands for the days of the week, Monday through Friday. Together, these four words form the heading of a calendar.