A freehub is a type of bicycle hub that incorporates a ratcheting mechanism.
A Shimano Dura-Ace freehub
A bicycle wheel is a wheel, most commonly a wire wheel, designed for a bicycle. A pair is often called a wheelset, especially in the context of ready built "off the shelf" performance-oriented wheels.
The front wheel from a racing bicycle.
Bicycle wheel with wooden rim
Nipples
Spokes