"Flush" here is used when something is at exactly the same level as a flat surface. For example, if you take two tables of the same height, and push them toget

"Flush" here is used when something is at exactly the same level as a flat surface. For example, if you take two tables of the same height, and push them together, their surfaces will be "flush". Or, if something is embedded inside a surface, so that it sits at the same level as the surface. The slot on some optical drives is a good example of a slot that is "flush" [1]. So on an ATM a "flush" slot would be one that is just a plain slot in the flat plastic surface of the ATM, without any anti-skimming device which sticks out the front. [1] https://www.dataquest.ch/images/uploads/newsimages/9056/usb_superdrive.jpg https://www.dataquest.ch/images/uploads/newsimages/9056/usb_...