Full Frame Sensor
The definition of a full size camera sensor is simply that it's the same size as a 35mm camera's film size(24mm by 36mm). Before digital photography arrived, all of the 35mm film was of one size. Now with digital photography, there are many options for size, regarding the sensor which has replaced film. There are also considerations about pixel density. Full frame sensors are good for landscape and architectural photography. You get great image quality and you get the full usefulness of wide-angle lenses. Compact cameras with smaller sensors don't give you as much background blur in portraits, because they give you more depth of field at the same aperture. One of the disadvantages of this larger size is that your lens and camera must be bigger too. This means heavier and more expensive.
One of the photography terms that is associated with sensor is crop factor If a sensor is full-size the focal length of a lens is the same as the lens would be on a 35mm camera. As you can see from the chart below, if your lens was a 105mm lens and you had a camera with an undersized sensor that has a crop factor of 1.6, then essentially that same lens will be like having a 168mm lens.
Smaller sized ones offer some advantages for telephoto photography because the smaller angle of view of small-sensor DSLRs enhances the telephoto effect of the lenses. For a more detailed explanation of Crop Factor and an illustration of it, read this article: Crop Factor Happy Shooting! Back from Full Frame Sensor to Digital Camera Instructions |
This article on full frame sensors is going to focus on the pluses and minuses of choosing a camera with a full sized sensor.
For a given number of pixels, the larger sensor allows for larger pixels that provide wider dynamic range and lower noise. Essentially that means a large size will give you a better quality on several fronts. 