Learner's definition of UPSIDE DOWN
with the top at the bottom and the bottom at the top
placed so that the end that should be at the top is at the bottom
You hung the picture upside down!
To remove the plant, turn the pot upside down and tap gently on the bottom to loosen it.
The baby was holding the book upside down.
turn (something) upside down
to make (something) very untidy
— often used figuratively