To the American Heritage Dictionary, a doodle is something scribbled while one is occupied. While I agree with this, I think a doodle is also a graphic depiction of the chatter in our subconscious. A graphic filtering of information, as you will clearly see in some of the doodles on this website. Much like our dreams may be sorting through the river of information we soak up in our lives, a doodle can do the same thing while we're preoccupied (usually on the phone, in class or a meeting.)

A doodle is not a drawing or a sketch. For those, you are consciously making an effort to create or depict something. You are occupied with creating your drawing.

A doodle, however, can start with something you can draw so easily that you're not aware of how to create it. For example, one of the first things I learned to draw as a child was a flower. The standard one, with a circle in the middle and 5-6 petals surrounding it. Add stem and stem leaves and you're done!

I can draw this flower as a base while I'm on the phone without even thinking. But as the conversation wears on,the flower usually turns into an organic-spaceship-y thing spilling around my page. 

Because I work in the design industry, it's common for me to have colored pencils strewn around my desk, so I tend to doodle in color...or color in my doodles when I'm not thinking:

So even though these floral doodles are recognizable, they grow out from my subconscious.  I'm not "cartooning" or trying to create anything pretty from them, my brain is just playing.  But for the best examples of true, subconscious doodles browse through the doodle gallery and have fun!