When you look at a map, you may notice that there are lines running both vertically and horizontally on the map, something like this:
The horizontal lines are called parallels of latitude. Some people just call them lines of latitude. The vertical lines are called meridians of longitude. They are also often just called lines of longitude.
Meridians of longitude are actually parts of circles that all go through both the North and South Poles of the Earth. It’s easier to see when you look at an actual spherical globe map, rather than a flat map like the one above. Here’s a globe showing some meridians of longitude:
Here’s a globe showing some parallels of latitude:
