title: what is the overlay line on each bar in a bar chart?
body: <p>I'm trying to learn myself with data visualization and when I'm going through the bar chart I'm stuck with the following thing.</p>
  
  <p>In  the graph there is a vertical black line on each bar in the bar char. What exactly signifies that overlay-ed black line. Thanks for your help </p>
  
  <p><a href="https://i.stack.imgur.com/lmor6.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lmor6.png" alt="enter image description here"></a></p>