What is the difference between 'Multiple Exposures' and 'HDR'?

I'm using Nikon, I know that Multiple Exposures means on the same frame, but HDR means multiple shots at different exposures combined in one frame. Is there any significance differences in the results between the two?

Multiple exposures are not unlike the typical double exposures we did when using film.

Many exposures on one image file.

HDR(i) is the combining or merging many identical images, except for the exposures to produce an image with very high dynamic range with detail in both the shadow and highlight areas

It is too bad you don't have the time to attend a proper photo course and learn all these things and much, much more

Okay so I'm going to have to make an assumption about a part of this…

Some of our cameras have a mode which in low light will take several shots at the same settings with very high ISO levels. The problem with high ISO levels is that images tend to be noisy, but by combining those multiple shots you can reduce the appearance of noise.So, it's multiple shots to reduce noise.

HDR on the other hand (and when done properly), tries to eliminate another issue that arises from sensitivity of the camera sensor. The issue HDR attempts to address correctly mapping the the total dynamic range of a scene. When you take a photograph it's often quite common that there will be areas in the image that fall off the too-dark and too-light range that the aperture and shutter speed allow for. So by adding under exposed shots you can map in more of the previously blown out highlights, and in overexposed shots map in more tone to areas that previously would have just appeared as black. Put it all together and you should get a richer all over tonal quality.

Multiple exposures are usually done for a creative effect, perhaps to show the same object at different angles or other ways. Usually, there's an intent for you to see the multiple effect.

HDR on the other hand is an algebraic computation of tone values only obtainable by several photos that are as close to identical as possible (other than the tonal values), so that you get an increased dynamic range. The intended result is to not see any multiple images.

Dynamic range is the contrast difference between the brightest and dimmest areas of the scene. When viewing the scene, your eye can see more range than film or digital photos (with film being better than digital). HDR tries to combine the limited tonal values of differently exposed photos to restore the natural dynamic range your eye sees.

Unfortunately, HDR has received a bad name by many that use this technique, as they over do it, to the point of the photo taking on a surreal nature. While I suppose there's some creative effect to this as well, it has been way overdone, and when most people think of HDR, they think of the surreal aspect of HDR.

HDR done right - in my opinion - would not have that surreal look to it, and would just increase the dynamic range enough to restore what your eyes naturally see without going overboard into the surreal.

I don't do HDR often, but when I do, that is how I do it.