Meridians and Parallels
The Meridian of any given place is that half of the meridian circle which passes through that place and both poles. A meridian of any place reaches from that place to both poles, and therefore is equal to one-half of a great circle, and, with the meridian directly opposite to it, forms a great circle called a meridian circle. There are as many meridians as there are places on the equator or on any parallel. Parallels are small circles which pass around the earth parallel to the equator.