Newell Posts
A newel, also called a central pole, is an upright post that supports the handrail of a stair banister. In stairs having straight flights it is the principal post at the foot of the staircase, but it can also be used for the intermediate posts on landings and at the top of a staircase. Although its primary purpose is structural, newels have long been adorned with decorative trim and designed with different architectural styles.

Reference:
Wikipedia