twelve o'clock

Short definition from Wiktionary

Noun

1. 1
   The start of the thirteenth hour of the day; noon (noontime); 12:00 p.m. (12:00).
2. 2
   The start of the first hour of the day; midnight; 12:00 a.m. (00:00).
3. 3
   A position straight ahead (horizontal clock orientation) or above (vertical clock orientation) (from the location of the 12 mark on a clock face)