eight o'clock

(In both the 12-hour clock and the 24-hour clock) The start of the ninth hour of the day; 8:00 a.m. (08:00).

(Only in the 12-hour clock) The start of the twenty-first hour of the day; 8:00 p.m. (20:00).

(informal) A position to the left and behind (horizontal clock orientation) (from the location of the 8 mark on a clock face)