it is the post (usually decorative) that holds the railing on a staircase or balcony.

that's a common term.... a good one for everyone who is not familiar with new construction to learn.... 

actually, complements parapet that you previously asked... 

I will go for the answer provided by Barbara Todaro. 

Ohh, I'm back on my game again ;)

I'm going with the railings on stairs.

I am pretty sure that is a dance move down the staircase. 

 Back to Wikipedia:  A baluster— also called spindle or stair stick^{[citation needed]}—is a moulded shaft, square or of lathe-turned form, a form cut from a rectangular or square plank, one of various forms of spindle in woodwork, made of stone or wood and sometimes of metal,^[1] standing on a unifying footing, and supporting the coping of a parapet or the handrail of a staircase.

Lots of great answers already here.

I am drinking my coffee on the balcony

A safety precaution for the balcony!

Dido to Marco,  thanks for your precision,  it is the post for a decorative hand rail. 

Hand rail.

Kenneth Jones got it. Not a real issue in Florida. Will use the term more now back in Chicago!

I had never heard of it prior, but looked it up.  Great question!