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 wouldn't be standing here if it wasn't for you and your beast. A bloody dead man tried to kill me. So you'll take it. I'll hear no more about it. - Is that understood? - Yes, my lord. Right. Now, don't think this means I approve of this nonsense with you and Alliser Thorne. That's a man's sword. (..)2011 TvShow: Game of Thrones Title: Baelor Season: 1 Episode 9