4R: 4 revolute joints.
Spherical: Joint center lines intersect at a common point.
Angle between center lines of revolute joints:
for the orange input link is γ = 20 deg.
for the green output link is β = 90 deg.
for the blue link is α = 90 deg.
for the base link is δ = 20 deg.
The output link revolves nearly regularly.
Its 1 rev. corresponds 2 rev. of the orange input link.