The word "ceilidh" is Gaelic and it means "visit" . The spelling used is Scots Gaelic but the meaning is the same in Irish. It from there expanded it's meaning to "house party" and is now used in English to equate to a concert setting where the music, both vocal and instrumental, would be Scottish/Irish or if you prefer Celtic.
What I don't understand is what you would consider the difference between a concert and a ceilidh, and why you would need two bands?
            Slainte,
                  Sandy