The symbol of the trefoil knot has known from ancient times as triquetra. Triquetra is a work derived from Latin tri- (three) and quetrus (cornered). Its original meaning was simply "triangle" and it has been used to refer to various three-cornered shapes.

In the mathematical field of topology, knot theory is the study of mathematical knots. While inspired by knots which appear in daily life, such as those in shoelaces and rope, a mathematical knot differs in that the ends are joined so it cannot be undone, the simplest knot being a ring.

A fundamental problem in knot theory is determining when two descriptions represent the same knot. A complete algorithmic solution to this problem exists, which has unknown complexity.