What do lines of latitude measure?

Lines of latitude measure north-south position between the poles.

Lines of latitude are imaginary reference lines that describe how far north or south a location on the Earth is from the Equator. The equator is defined as 0 degrees, the North Pole is 90 degrees north, and the South Pole is 90 degrees south. Lines of latitude are all parallel to each other, thus they are often referred to as parallels.