A helix is a three dimensional spiral shape. Helical is the description given to something with this shape.

This is a fairly important shape in Robotics.

It is the shape left/created in a fluid or medium by a Propeller blade, and the basis of the design of Impeller or Propeller blades.

It is also the natural shape of DNA - our Genetic material.

Helical Gears are important - and offer mechanical advantages.

Screws and Bolts are essentially Helical.