The equator or the axis is what you're thinking of
it is called axis,z
The Tropic of Capricorn passes through Botswana.
The axis is the imaginary line that a planet rotates about, The earth's axis passes through the North and South poles.
The earth rotates on it's axis, the imaginary line that runs from the north pole to the south pole through the center of the earth.
the earth's zero of longitude, which by convention passes through Greenwich, England.
The horizontal line that goes around the "waist" of the Earth is the Equator. The vertical line that goes vertically around the Earth, through the poles, is the Prime Meridian.
The axis is an imaginary line that passes through the North and South poles. The Earth rotates on its axis, completing a full rotation each day.
the imaginary line that passes through the earth's north and south pole while it rotates
a latitude line
The Tropic of Capricorn passes through Botswana.
prime meridian
The axis is the imaginary line that a planet rotates about, The earth's axis passes through the North and South poles.
Tropic of Capricorn
In astronomy it is called the axial tilt (also called obliquity) and sometimes just called the imaginary axis.
the tropic of Capricorn
An imaginary line which passes through the poles of the planet.
the axis
You may be thinking of the Prime Meridian and the International Date Line.