You've heard the term 'Complication watch', but you're not sure what that is?
If a mechanical watch offers more functions than just the time (hours, minutes, seconds), then it is considered a 'complicated' timepiece. Each 'extra' function next to hours and minutes is then called a complication.

Some of the more known complications are:
MoonphaseThis Complication shows the current phase of the moon in the lunar cycle.Perpetual CalendarThis Complication adjusts the calendar for month length and leap years.FlybackThis Complication makes the Chronograph reset and restart in one push of the button.DateThis Complication displays the Date on the watch.AlarmThis Complication have a dedicated alarm and alarm hand.Panorama DateThis Complication means the watch has a big date display.Power ReserveThis Complication means the watch has a power reserve indicator.