User blog comment:Penguin-Pal/How to create buttons/@comment-32129972-20121221024553/@comment-4018164-20121226161906

Bitmap images are presentations of dots (pixels), that each one of them has a color value.

Vector images (.svg) are not saved as a layer of pixels, but as a document with vectors- paths, circles, rectangles and other shapes, that is converted to pixels when displayed in your screen.

It has a really major pro, as you can keep resizing it, and as it's made from vectors and not pixels, your browser will display a larger quality in your screen.

Here is a comparison between a bitmap and an svg image:

http://upload.wikimedia.org/wikipedia/commons/6/6b/Bitmap_VS_SVG.svg