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.
(..) I'm sick of being a clown, sick of play-acting. It's happening way too often. I can't keep hamming it up for TV crews. Is that understood. I don't want them anymore. I'm surrounded by assholes! Don't forget it. I'm a Ferrari. You open the hood with white gloves! (..)2016 Me Before You