Painting or Illustration

   So what exactly makes a painting a painting, and what makes an illustration and illustration? After graduating from an art school, I am still befuddled by the distinction of their terms.
   Is an illustration something more commercial, and a painting less commercial? But they are equally prevalent in the media so whats the significance of coining the terms? Just for the sake of organization I would like to label my more experimental, abstract work as paintings/ drawings, depending on the medium. All of my more commercial looking work will be labelled as illustrations. I hope this will be a better approach than labelling everything depending on its medium. I'll also try and consistenly tag each piece of work, with its coresponding size and medium for the painting, drawing and illustrations.