A Volute spring is a compression spring in the form of a cone (a Volute). Under compression, the coils slide past each other, thus enabling the spring to be compressed to a very short length in comparison to what would be possible with a more conventional helix spring.
The shape of the initial spring steel (or other material) is a "V", with the ends of the V at either end of the wound spring (which forms a distorted cylinder, of wider diameter at the centre), and the bottom point of the V at the centre.
Such springs can frequently be found as a component of garden secateurs. Short posts anchored in each side of the handles, and inserted into each narrow end of the spring, retains the spring in position.