Hasse's theorem on elliptic curves

Hasse's theorem on elliptic curves, also referred to as the Hasse bound, provides an estimate of the number of points on an elliptic curve over a finite field, bounding the value both above and below. If N is the number of points on the elliptic curve E over a finite field with q elements, then Hasse's result states that | N − ( q + 1 ) | ≤ 2 q .