Perigean spring tide refers to the highest tide that occurs during the new and full moon phase. It is caused by the gravitational pull of the moon and the sun being in alignment with the Earth. Synonyms for perigean spring tide include highest astronomical tide, perigean tide, spring tide, and syzygy tide. Other related terms include apogean tide (when the moon is farthest from the Earth), neap tide (when the sun and moon are at right angles to each other), and tidal range (the difference between high and low tide). Perigean spring tides can cause coastal flooding and are important for marine life and ecosystems.