What is the term for unusually high or low tide due to astronomical influences?

The term for unusually high or low tides due to astronomical influences is known as a spring tide. Spring tides occur when the gravitational forces of the moon and sun align, which happens during the full moon and new moon phases. This alignment results in higher high tides and lower low tides, creating a more significant tidal range.

In contrast, neap tides, which occur during the first and third quarters of the moon, result in a smaller tidal range because the gravitational forces of the moon and sun are at right angles to each other. High tide and low tide are simply terms denoting the peaks and troughs of the tidal cycle and do not specifically refer to the amplified effects brought on by astronomical alignments. Therefore, spring tide is the correct term indicative of these extremes in tide levels due to the interplay of lunar and solar gravity.