High-end, live-preview digital cameras are referred to as either bridge or prosumer digital cameras. While DSLR cameras operate on the same mechanical principles as the autofocus 35mm film single-lens reflex camera, the key difference is that a CCD or a CMOS image sensor takes the place of the film. This allows for creation of images in-camera without the need to chemically develop an image on actual film.
The major advantage over other digitals is the defining characteristic of an SLR: the light goes directly from the main lens, instead of reflecting from an off-axis viewfinder.
The advantage of seeing an exact copy of the image has been duplicated in the LCD displays of many of the digital compact cameras. However, the SLR retains the best quality of image due to its being in real time and more detailed.
LCD displays tend to have a time lag, causing the view to be clear, but not exactly what you are looking at. If something in the shot is moving, this movement will actually be viewed a second or two later. While bridge cameras are comparable in weight and size to the smaller dSLR they lack the mirror and reflex systems which are characteristics of dSLRs.
Referred to as "bridge" cameras because they hold a place between the digital consumer compacts and the dSLR's, prosumer identifies their high-end more advanced technology.
The lines between the two are not clear-cut -- the LPD category includes both the bridges and compact cameras. Mainly they both have live-preview on an electronic screen, which is their principle means of previewing an image before taking the photograph. There are also several nonessential characteristics applying to many of the bridge cameras, but not all of them.
For instance, there is the single fixed noninterchangeable lens and a CCD sensor, which is much smaller in the bridge cameras than in the dSLRs. A few of the new bridge cameras have defied these nonessential qualities and now have larger sensors of different types that are equal in size to those found in some of the dSLR cameras.
Bridge cameras still do not have interchangeable lenses; however, this may change in the not too distant future.