An
ass app is terminology commonly used by graphic designers when having to urgently create
something from scratch or figuratively 'pull it out of your
ass.'
Client: "Oh, we love the
ad campaign but would like to make a few changes. Could you
change the photo, rewrite the copy and have it to the publisher in an hour?"
Graphic Designer: "Sure! No problem. Let me use my
ass app and I'll have that ready in a jiffy!"