Super noob-question, but see the green 'confirmation' dialog box in the image below? Is there a technical name for that element? (Or is it just called a 'dialog box', or the like?)

My site's having problems with lightbox confirmation screens for things like "Your message has been sent", or "Your changes have been saved"...and I've seen this type of element on other sites, where instead of spawning a lightbox, submitting a form will spawn this sort of 'dialog box' (pushing all of the page's content down)...and sometimes the dialog box will stay on screen (until the page is refreshed), whereas other times it will slide closed dynamically after a few seconds. I just want to know the technical term for it so I can learn more about it.