A newel base is the bottom part of a newel post, which is the vertical support pillar in a staircase.
The newel base is the section that is anchored to the floor or the stair tread.
It provides a stable foundation for the newel post & helps ensure that the newel post is securely attached and can bear the load and stress placed on the staircase, particularly at the points where the railing turns or ends.
Oak 
Pine