Barbara Todaro although Jeff Dowler has the technically correct answer, we all know that the real reason the post is at the end of the stairs is to support the newel cap.  That cap is all important to keep the kids that slide down the railing from flying off at the end!  

Stop!  Sometimes in the name of love too.  

Anchors the handrail & the last place where you hit your head after falling down the stairs. Usually quite substantial so you really feel it.

It anchors the railing. Hi btw-I was thinking of you @the beach today

Lisa Von Domek nailed this one!

My college boyfriend's name was Newell.  Turns out he wasn't needed.  LOL

Barbara Todaro It's the post at the bottom or top of a staircase. I do like Lisa Von Domek 's answer.

That's something 'Newell'!

Have you taken over for Tony and Suzanne Marriott, Associate Brokers ?

You only need on if you don't want your stair rail to come tumbling down.

Lisa Von Domek gets my vote!

I thought you were talking about a blogger on ActiveRain.   Never mind.

Main stablizer/anchor  for pickets / handrail.

It is a staircase part and is the larger post that supports the handrail.

It's the main post of a stairway banister that anchors the handrail. I think it's also the central post in a sprial staircase

If the owelled one is baroque!

I learned from the answers.

Anchor post! Again, as usual, late to the party!

The posts that support the hand rail.

Barbara Todaro - few good answers - and now I know about Newell Post...

WEll,  know that a few kids have hurt something not stopping in time when sliding

Thanks for another good question Barbara Todaro 

Many of the answers here remind me of my childhood home with staircase that we secretly slide down.  Thank goodness all the right parts were in place and we all lived to tell the story in later years, of course. If our parents knew how many times we slide down we might not be here today.

This is part of the staircase. 

An item that was added to my vocabulary tonight.

When i was younger it would be what stops me when i slide down the railing. I do see many a loose Newell posts in older homes. Perhaps from years of just that