The osculating plane is the plane containing the tangent vector $\mathbf{t}$ and the principal normal $\mathbf{n}$ at a point on a curve. It is the plane that most closely approximates the curve near that point. The binormal $\mathbf{b} = \mathbf{t}\times\mathbf{n}$ is perpendicular to the osculating plane. The normal plane contains $\mathbf{n}$ and $\mathbf{b}$; the rectifying plane contains $\mathbf{t}$ and $\mathbf{b}$.