What are the differences between a bridge camera and a D/SLR?
The main thing about a Bridge camera is that it's "Bridging" the gap between a small point & shoot camera, and a larger DSLR.
So the comparison of a bridge camera to a DSLR comes down, basically, to the following:-
A good article on Bridge cameras can be found here.
From personal experience, my old Boss once asked me about some issues he was having with his Fujifilm Bridge camera. Indoor photos of his daughter, when viewed at 100% had absolutely horrible red marks all over the photo - especially in the skin tones. So much so that even viewing at a reasonable smaller size on the monitor resulted in noticable red 'grain' in the photo. I took the camera and tried lots of things with it, but was unable to correct the fault. He asked me for a recommendation and (at that time) I suggested the Canon Powershot S90. He got one, and never had any problems with the photos from it. So if you are considering a Bridge camera - it may be worth instead to look at a high-end compact instead.
As an aside I once heard it said that with Bridge cameras you essentially get the disadvantages of both systems -- the size and weight of a DSLR and the lack of flexibility of a point & shoot. I quite like the saying, but it's an individual viewpoint. Many people have Bridge cameras and are very happy with them.
I actually had to do a quick google on "bridge camera" - but I'd say the differences are rather obvious:
Bridge Camera = high end point and shoot
It's important to realize that "bridge camera" is not a technical term. It's a marketing term *, made up to sell more-expensive cameras to intermediate photographers who are beyond point and shoots but are intimidated by the cost or complexity of a SLR.
Generally, the things sold as bridge cameras are bulky point and shoots which kind of look like they might be an SLR. Usually, they have superzoom lenses built-in. Somewhat ironically (or maybe just unfortunately), this isn't what someone who really wants a bridge in learning about photography needs.
There's a little more on this in the answers to this question Is there any bridge camera with an interchangeable lens? (To which the answer is: by definition, no.)
I think this term is particularly obsolete this year, with a new crop of crazy-cool intermediate cameras that are definitely not point-and-shoot in the sense of no control or advanced functionality. The new Canon G1 X, which has a large (basically micro-4/3rds sized) sensor but a non-interchangeable zoom lens is a poster-child for this, but also pretty much all the lower-range mirrorless interchangeable lens cameras too. Basically, there's a whole bunch of advanced cameras which are not DSLRs but definitely not point and shoots either. One could apply the term "bridge" to all of these, but I don't think it's very useful.
I recommend ignoring this term and talking about specific cameras (or groups of cameras — all the small-sensor superzooms are basically identical) or specific features (like a large sensor in a compact camera body).
* See newspaper article from 1998 about the "new" type of camera.
It's all about the lens. Looking at the cameras which are called a bridge camera, the first thing you will notice is the big honking lens on the thing, I think the rest of the features can be compared with point and shoots but not this one. That's its most distinguishing feature whether or not it makes it compare to an SLR is a matter of opinion.