Syzygy

A near-straight alignment of three celestial bodies, such as the Sun, Earth and Moon at new or full moon.

In the Earth–Moon–Sun system, syzygy combines lunar and solar tide-generating forces and is associated with spring tides, which have a greater-than-average tidal range. Exact local tides remain shaped by basin geometry, depth and weather.

Syzygy is also the geometry required for solar or lunar eclipses when the bodies align closely enough with the orbital nodes. Not every new or full moon produces an eclipse.