Baluster/Spindle: A member that runs from the bottom rail/floor to the top rail. 

Rail Post: The vertical componenet that supports a railing.

Top Rail: The top piece of the rail that runs from post to post.

Bottom Rail: The bottom piece of the rail that runs from post to post. 

Drink/Cap Rail: A piece that is place on the top rail for a decorative finish or to provide a wider surface for a place to rest drinks. 

Hand Rail: The top rail/ or a secondary rail that is designed to be held by a person when navigating the stairs. It is usually at waist height. 

Rail: The combination of top/bottom rail and balusters/spindles.

Post Cap: A decorative piece that fits over the top of the post. 

Post Skirt: A decorative piece that covers the connection point between the post and the surface it is attached to. 

Level Railing: A railing that is installed on the edge of a landing/deck or other level surface. 

Stair Railing: A railing that is designed to be installed at an angle for stairs.