File:Tangent.secant.png

"Some map projections contact the earth's surface along a point or line, called a tangent, while other map projections contact the earth's surface along two lines, called secants. Both tangents and secants represent locations on the map projection where there is no distortion". http://www.geography.hunter.cuny.edu/~jochen/GTECH361/lectures/lecture04/concepts/Map%20coordinate%20systems/Tangents%20and%20secants.htm