Meaning of high-water mark

high'-wa'ter mark"

Pronunciation: (hī'wô'tur, -wot'ur), [key]
  1. a mark showing the highest level reached by a body of water.
  2. the highest point of anything; acme: Her speech was the high-water mark of the conference.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.