What does it mean "out of blue"?

In my opinion: it have means 1)From an unexpected or unforeseen source. e.g. critism that came out of the blue. 2)At a completely unexpected time. e.g. arrived out of the blue.

Basicly in my opinion the Phrase "out of the blue" means that something happened very unexpectantly. For instance lets say someone who you havent seen or talked to in a few years just all of a sudden shows up at your door im gonna use the name bob as an example. Youd say something like " Bob showed up at my house today out of the blue"

i cannot know