Here what this band basically means. A single protein or many proteins exist along the following region. And all these proteins basically have the same exact isoelectric point, the same exact pi value. And the same thing is true for these other bands, as shown. Now, if we take this horizontal slap and we place it into our SDS Page setup, we can now separate our proteins based on size. So this is one direction, the horizontal direction of separation, and this is our vertical direction of separation.