Can someone tell me what a blu ray disc is?

How is it different from a dvd?

The difference between a dvd, hdvd, cd and blue rays are merely technical. It is all about the laser and how the information is stored and maybe the material used to make the disk. A dvd uses a red laser. A blu ray uses a blue laser. The blue laser is at least half the size of the red laser meaning that you can stored double the information or more in the same space. The difference is like using a crayon and a color pencil. You can color a more detail picture with the color pencil because the tip is smaller. There might be other difference in the way the information is written to the disk but I'm not sure.

Remember that most of us do not need to know all the details to use the product. Only people that build the product or products that are going to use the blu ray need to know the exact nature of the beast. What the average user need to know are 2 things. 1) is that the more information you can squezed into an area the better a picture or movie "MAY" look. Remember that the fact that you saved a picture or movie to a blu ray will not improve it. What it will do is that you can put more information in it so the level of detail can be better. IS like saving a picture in high resolution. The higher the resolution the more details you can see. Especially when you zoom into it. The drawback is the size of the file so people compromise by getting a picture that is good enough as opposed to the best quality posible. 2) the other thing to know is that devices have to be made to handle this new format. You cannot play a blu ray movie or an hdvd on a regular dvd because the device or dvd player was not built for this in mind.