What does the upper right 'Close' button do? Does it end editing or does it close the form so it does not work anywhere?

What does the upper right 'Close' button do? Does it end editing or does it close the form so it does not work anywhere?

It would be great is there was a 'hover' text that popped up explaining exactly what each button actually does.

Hover over 'Close' and it would say 'Click to Close this form to end editing' or 'Click to Close this form's items from working'.

Sorry for the repetition - I just posted the same question about the 'Lock' button.

I know this is a dumb question to an experienced user but I can not find a simple answer in the software.