When people say “they're engaged,” the phrase “to be married” 'is understood'. [=“they're engaged” is understood to mean “they're engaged to be married”]
We still don't fully 'understand' the causes of the disease. = The causes of the disease are still not fully 'understood'.
He believed it 'was understood' [=believed that everyone had agreed] that he would be paid for the work.
(..) That's great. It's alright. Truth is, I don't think people... understood what it was I was doing at Shaffer. I wasn't there to conduct. Any fucking moron can wave his arms and keep people in tempo. I was there to push people beyond what's expected of them I believe that is... an absolute necessity. (..)2014 Whiplash