The correct answer is A) the difference between the depth of the water and the area's tidal datum. The height of tide refers to the vertical distance between a specific water level and the tidal datum, which is a standard reference point. The tidal datum is the average of high or low water levels over a specific time period, usually 19 years. The height of tide is therefore the difference between the current water depth and this established tidal datum. The other options are incorrect because they do not accurately describe the height of tide. Option B refers to the tidal range, option C confuses the height of tide with the high water level, and option D describes the depth of water at a specific time, not the height of tide.