The answer is simple. It's called the equator, for the longitude it is called prime meridian.
The equator is at 0 degrees latitude.
equator
Equator
The Equator
The equator.
The Equator
The Equator.
The Equator.
0 degrees longitude
In terms of geography, 0 degrees longitude is known as the Prime Meridian. 0 degrees latitude is the equator.
The Prime Meridian is the line whose longitude is defined as zero. The equator is the line whose latitude is defined as zero.
The zero (0) degrees of latitude is the Equator.