One of the times on the clock: eight o'clock (hachi-ji). Context determines whether it's a.m. or p.m.
映画は８時に始まるから、７時半に出発しよう。
The movie starts at eight, so let's leave at 7:30.
朝８時までに会社に着かなければならない。
I have to be at the office by 8 a.m.
８時ちょうどにアラームが鳴った。
The alarm went off at exactly eight o'clock.