mean high tide. The average of all high tides, esp. over a period of 18.6 years.
— Also termed ordinary high tide.
mean lower low tide. The average of lower low tides over a fixed period.
mean low tide. The average of all low tides — both low and lower low — over a fixed period.
neap tide (neep). A tide, either high tide or low tide, that is lower than average because it occurs during the first or last quarter of the moon, when the sun’s attraction partly counteracts the moon’s.
ordinary high tide. See mean high tide.
spring tide. A tide, either high tide or low tide, that is higher than average because it occurs during the new moon and full moon.