What is this screen in vim?

When using vim, I sometimes get myself into this screen that has multiple command line rows. What is this screen for? How do I take advantage of it or get out of it?

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Solution 1:

That is the command line history window. Check here.

It appears when you type q: (you also have a search history if you type q/). This windows allows you to edit your command and search history. Press ctrl + c twice to cancel.