No question is dumb if you want to learn- orbital is circular, like a moon around a planet/ random is not always in the same positin- thus random orbital goes aound in a circle but because of a centifugal weight, also back and forth. This way it covers more area in a single pass and also does not dig in as bad as you are not concentrating the abrasive in only one spot. Same as DA/ Dual Action- in a circle and back and forth.:thumbup:
All DA's that I have seen have a way to lock them so they are either random orbital, or simply circular, like a grinder. I am not one of the college educated type, but I believe that is why it is called a DA (Dual Action).
They are called DAs because they have 2 separate actions running at the same time - while the big wheel goes around in big circles, the other action makes it go back and forth in little circles - the smaller the circles, the finer finish it will do. Quality sanders are available with different sized orbits.
A lot of DAs have a lock but it is intended to lock one action so you can change the sanding pad. If you run them locked, they tend to vibrate.