1. A tide of decreased range that occurs twice a month, when the moon is in quadrature; that is, during its first and last quarters, when the sun and the moon are at right angles to each other relative to the earth.
2. The tide raised on the earth when the sun and moon are in positions forming a right angle at the earth's center.

The two pulls (sun and moon) largely cancel each other out, resulting in an extra low high tide and an extra high low tide.