I've figured out what sourdough and bread really are...
I've been doing a lot of thinking lately, and here's what I've come up with:
Sourdough: A device made from flour and water used for cultivating natural yeast.
Bread: A balloon like device made from usually wheat flour and water used for capturing "yeast farts".
So based on this definition, bread is a "Yeast Fart Balloon".