Ccd's and in large telescopes

reflecting telescopes

Basically, the catadioptric telescope is just one of the 3 main types of the optical telescopes.The other 2 main types of optical telescopes are the refracting telescopes and the reflecting telescopes.

No. Radio telescopes are the largest, consisting of multiple (sometimes hundreds) of dishes tens of metres across in enormous arrays.

"Optical" simply means that they work with visible light - as opposed to other EM radiation (radio waves, x-rays, etc.); gravitational waves; etc.