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 it hit me. I saw it... almost like a light bulb going off above my head. Where does the real power lie? The power behind the power. And I understood, Claire, that we have to think and act differently than we ever have. Because it's no longer about who lives in the White House... (..)2017 TvShow: House of Cards Title: Chapter 65 Season: 5 Episode 13