I don't really know myself. You should look at : wikipedia
But the general idea is :
- recording an analog video on digital support. As the support is digital, you can also record analog or digital sound on the disc.
The technology is interesting. And the result also.
If you want to see a movie like a similar copy of theater projection (but in low resolution), then laserdisc is the solution. If you want a digital restoration, clean image, no blur, artificial looking, go to the DVD/Blu-ray edition.
I started Laserdisc when I saw Starwars episode IV, V, VI the first time in Blu-ray. I thought : no, it's impossible. Starwars was not like this. After some research I found why, and how to watch the original version.
LDDB : the best website ever about laserdisc. The database is perfect, and the community is great!
Not on Blu-Ray : a very good website with tests of some LD players
Laserdisc archive : the best website about LD players ! All players in details.
Laserdisc plaza : good site in french. Don't know why, but french people loves LD !