An optical bench is something you would find in a research lab. It is a flat,sturdy table that you can experiment with light on. For example, you might have a laser on it, with some mirrors and lenses and such to study how light refracts, or reflects or any other interesting thing you might want to do with light....
Mirrors, lenses, prisms, color filters etc are all available with mounts to go on the bench so you can arrange them however you like to do whatever it is you are doing with light...
The mirror above is 'front surface', meaning the silvering is on the side you are looking at , instead of the back. Normal mirrors put the silver on the back so the glass will protect it, but that means the light reflected in the mirror has to pass through the glass twice, and some of the light is lost in the process, and the color changes slightly.
For precision mirrors, the silver is on the reflecting side so that doesn't happen. (however, it is not protected, so the mirrors are very easily damaged)
