The Arithmetic of Elliptic Curves
《The Arithmetic of Elliptic Curves》 · 第 145 页 · Chapter V，Section 3「The Endomorphism Ring」，Definition
If $E$ has the equivalent properties given in Proposition V.3.1(a), then $E$ is supersingular, or has Hasse invariant $0$. Otherwise $E$ is ordinary, or has Hasse invariant $1$.