""am" is before the meridian. "pm" is after the meridian"."
It doesn't matter what the letters technically stand for, it's a simple naming convention that is well established and easily understood - 12AM is midnight, 12PM is midday. Also, 2400 is perfectly valid and often used in place of 0000. While there are plenty of arguments about ordering of dates and the like, I'm not aware of any alternative conventions for the above; people complaining about them being silly or hard to understand just need to make the tiny effort to learn something most of us had grasped before we left primary school.