What is "tricolorability"

In the mathematical field of knot theory, the tricolorability of a knot is the ability of a knot to be colored with three colors subject to certain rules. Tricolorability is an isotopy invariant, and hence can be used to distinguish between two different (non- isotopic) knots. In particular, since the unknot is not tricolorable, any tricolorable knot is necessarily nontrivial.