Definitions for "Mean sea level"
Keywords:  msl, tide, hourly, datum, midway
MSL) Sea level at its mean position, midway between high and low tide, adopted as a standard for the measurement of heights.
Elevation datum referenced to averaged sea level observations over an extended period of time.
A tidal datum. The arithmetic mean of hourly heights observed over the National Tidal Datum Epoch. Shorter series are specified in the name; e.g., monthly mean sea level and yearly mean sea level.