OR NOT SO BLACK ...
Most people think the easiest way to try to remember the difference between vector and raster is, vector is artwork, raster is imagework. That's a very simplified version of the true story.
Vector is an algorithm which produces a figure that will be a perfect specimen, no matter how closely you zoom into it. Think of it as a solid mass, which is usually a solid color or gradient tint. Vector has a plus in that it is equipped with editable points called "Beziers" which allow you to edit the figure as if you were editing a solid mass, easily changing the shape of the item as a whole. In a large, complicated piece of artwork this can also be a drawback, in that each individual section must be edited separately in order to change small specifics of the art.
Raster is millions of pixels that blend with each other to form an image. A small file embedded in the image file tells the program how to arrange these pixels. If you've ever zoomed in on a low resolution web photo file, you will understand. Each individual dot holds a single color and, depending on the density of the dots (DPI, dots per inch) it will determine just how pure the image will be. Many filters or effects can be applied to a raster file to enhance or change it drastically or subtley, regarding just about anything you can imagine.
Of course, a perfect image is a raster file that is so high in resolution, that when "vectorized" will look just like the photo. My personal scanner goes up to 12800 dpi, but of course, the initial item must be comparable to that resolution in order for it to make any difference (GI/GO).
Sorry to borrow from Wiki, but this is a perfect example of the difference between vector vs. raster. The full article is here:
As in the example below, we can also print two colors, but they cannot be blended colors. They must be separate. If you send Illustrator Vector files, please assign PMS colors to your artwork.
The samples are just "for show." They are not at the proper resolution and are saved for the web. Web files are usually low resolution files so that they will load quickly onto a web page. We do NOT accept web files of ANY kind.
If you notice the image of the bottle on the left (the vector version is on the top), you will see that it is clean. No matter how close you zoom in, it will not change the appearance of the artwork. The bottom version is the "bitmap" or raster image. This can change depending on how high your resolution is set, and my guess is with this item, it's set to optimize on the web at 72 dpi.
The above image depicts what a vector image is, showing the Bezier points and editing handles.
Here is the excellent essay on vector graphics from a very talented artist named Brian P. Lawler (the above image was taken from his piece)
Here is Brian's website where he also has other free graphics essays: