Latitude measures how far a place is north or south of the equator. Its lines (parallels) run east–west; values range from 0° at the equator to 90° at the poles, and the spacing between parallels stays roughly constant.
Longitude measures how far a place is east or west of the prime meridian (0°, through Greenwich, England). Its lines (meridians) run north–south from pole to pole; they are farthest apart at the equator and meet at the poles, with values from 0° to 180° east or west.
Together, latitude and longitude form geographic coordinates that pinpoint a location on Earth. Source: NOAA National Ocean Service.