Motion smoothing is also known as motion interpolation, video interpolation, and the soap opera effect, it refers to a process of reducing motion blur by artificially inflating the frame rate of the film or series.  

• So, from 24 frames per second (fps) it is increased to 60fps, 120fps or even higher (higher rates are perceived as motion), digitally combining the images to simulate more.  
• This effect can be useful when watching sports, as the action moves quickly, and enabling the feature allows viewers to catch more details. 

Source: The Hindu