the beginning of something's existence or use, the arrival or introduction of something;
e.g. Since the advent of this technique, countless lives have been saved.
(noun)
the coming or second coming of Christ, the period of time that begins four Sundays before Christmas and is observed as a season of fasting and prayer by some Christians (used as Advent);
e.g. Their family observes Advent as a time of celebration.
(noun)
the arrival or appearance of an important person;
e.g. They are awaiting the advent of the chief guest of the event.