Spring tide, tide of maximal range, near the time of new and full moon when the Sun and Moon are in syzygy—i.e., aligned with the Earth. Conjunction is the time during new moon when the Sun and Moon lie on the same side of the Earth. The other syzygy condition, opposition, occurs during full moon.
When the gravitational effects of the Sun and the Moon combine, we get spring tides, which have nothing to do with the season of spring. The term refers to the action of the seas springing out and then springing back. These are times of high high tides and low low tides.
Spring tide essentially is the two tides where the sea is at its most extreme: the highest and lowest. In contrast, a neap tide is one where the difference between the high and low tides is at its lowest.