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.
(..) 'cause I won't understand? Both. Okay, now I really want to know. He's laying down a new dubstep track, and I need to write a program for him. - I understood "him." On a scale of to , how much do I embarrass you? - Excellent. Hey, you finish your English paper yet? - Uh, in theory. (..)2016 TvShow: Designated Survivor Title: Pilot Season: 1 Episode 1