Hello Sideeq !

The 180th degree meridian ( A meridian is an imaginary line that connects all the locations that have a certain longitude ) is also called the anti meridian.

It is used to define the International Date Line. Because the Earth is spherical, traveling 180 degrees in either direction from the prime meridian will lead to 180 degrees longitude or the opposite meridian.

That is the meaning of 180 degrees of latitude : Traveling 180 degrees in either direction from the prime meridian.

Hope it helps !