The Theodorus spiral, also known as the Einstein spiral, Pythagorean spiral, square root spiral, or--to contrast it with certain continuous analogs--the discrete spiral
of Theodorus, is a discrete spiral formed by connecting
the ends of radial spokes corresponding to the hypotenuses
of a sequence of adjoining right triangles. The
initial spoke is of length , the next spoke is of length , etc., and each segment of the spiral (corresponding
to the outer leg of a triangle) has unit length.

The slope of a continuous analog of the discrete Theodorus spiral due to Davis (1993) at the point is sometimes known as Theodorus's
constant.