limaçon

right|thumb|300px|Construction of the limaçon with polar coordinates' origin at

In geometry, a limaçon or limacon , also known as a limaçon of Pascal or '''Pascal's Snail, is defined as a roulette curve formed by the path of a point fixed to a circle when that circle rolls around the outside of a circle of equal radius. It can also be defined as the roulette formed when a circle rolls around a circle with half its radius so that the smaller circle is inside the larger circle. Thus, they belong to the family of curves called centered trochoids; more specifically, they are epitrochoids. The cardioid''' is the special case in which the point generating the roulette lies on the rolling circle; the resulting curve has a cusp.