Vector images are made up of many individual, scalable objects. These objects are defined by mathematical equations rather than pixels, so they always render at the highest quality. Objects may consist of lines, curves, and shapes with editable attributes such as color, fill, and outline. Changing the attributes of a vector object does not effect the object itself. You can freely change any number of object attributes without destroying the basic object. An object can be modified not only by changing its attributes, but also by shaping and transforming it using nodes and control points. Because vector-based images are scalable, they are resolution independent. You can increase and decrease the size of vector images to any degree and your lines will remain crisp and sharp, both on screen and in print. Fonts are a type of vector object. The image below shows the difference between vector image and raster image when they are increased in size. Vector images are not restricted to a rectangular shape like bitmaps. Vector objects can be placed over other objects, and the object below will show through. See the example to the right. The vector circle and bitmap circle appear to be exactly the same when seen on a white background. But when you place the bitmap circle over another color, it has a rectangular box around it, from the white pixels in the image. Vector images have many advantages, but the primary disadvantage is that they’re unsuitable for producing photo-realistic imagery. Vector images are usually made up of solid areas of color or gradients, but they cannot depict the continuous subtle tones of a photograph. That’s why most of the vector images you see tend to have a cartoon-like appearance. Vector images primarily originate from software. You can’t scan an image and save it as a vector file without using special conversion software. On the other hand, vector images can, quite easily, be converted to bitmaps. Meta files are graphics that contain both raster and vector data. For example, a vector image that contains an object which has a bitmap pattern applied as a fill, would be a metafile. The object is still a vector, but the fill attribute consists of bitmap data. Source.