In classical music, "Common time" is 4/4, that is four beats to the measure with a quarter note getting one beat.  I'm broadening the term to refer to any kind of rhythm that can be counted in multiples of two.  You could also call it duple time.

Triple time is then any rhythm that has multiples of three.

I am going to work up to finger picking soon, not quite there yet. Thank you for explaining the rolls. I still need to buy some finger & thumb pick.

The term "common time" is new, can you explain please?

By the way, you really have some nice dulcimers.