Concordance happens when everything agrees. It can refer to an agreement of opinions, or it can describe things that are in harmony. Your words may be in concordance with your actions — that means they're expressing the same thing.
Concordance traces back to the Latin word concordans, meaning "being of one mind." When things are in concordance, it's as if they're of one mind: they agree or are in harmony. A talented home designer will remodel an interior so there's concordance from room to room. If you're a scholarly type, you might already know concordance can also be a list the main words in a book, usually linked to the passages where they occur.