Question

Every 18 months, during the Spring tide, the Moon is at its closest distance to the Earth, called its what

Answer 1

When the moon is closest to the earth, it is called a super moon.
Also known as a perigee this happens because of the moons gravitational pull towards the earth when the eccentric lunar orbit brings the perigee closer.
Tides raise (perigean spring tides) due to the excessive pull of the moon, at which “pulls up the ocean.”