Latitude lines are parallel, circling the globe like the equator. The longitude lines, on the other hand, are the ones that meet at the poles. Latitude is the position of someone or something in relation to the equator. The longitude coordinates are the position of someone or something in relation to the Prime Meridian, or the middle of the globe going around the poles.
Latitude and longitude are most often used as coordinates by sailors and scientists. They are exact coordinates, and can easily be found on the globe, if you know where to look. Once someone has the right longitude and latitude coordinates, they can find anything on the globe: the White House, the Capitol building, the Taj Mahal, etc.