Spring tide is a term used to describe the tides that occur when the gravitational pull of the sun and the moon are aligned and reinforce each other, resulting in higher high tides and lower low tides. Spring tides occur twice each lunar month all year long, without regard to the season. The term "spring" has nothing to do with the season of spring, but rather is derived from the concept of the tide "springing forth".
Neap tides, on the other hand, occur when the sun and moon are at right angles to each other, partially canceling out each others gravitational pull and resulting in moderate tides.
A perigean spring tide is a tide that occurs three or four times per year when a perigee (the point nearest Earth reached by the Moon during its 27.3-day elliptic orbit) coincides with a spring tide. This has a slight but measurable impact on the spring tide, usually adding no more than a couple of inches.
