A spiral is a curve which turns around some central point, getting progressively closer to or farther from it (depending on which way you follow the curve). In polar coordinates, then, r is an monotonic function of θ.
Some of the more important sorts of spirals include:
... the device, is a little wider than the axis, and the gyroscope's evasive action towards the externally applied force will cause one end of the axis to push against the ...