Although Maja's answer is perfectly valid [save for the XR abbrev.], I'm here offering a very US-specific term used when referring to plain abdominal radiographs: Kidney, Urethers, Bladder (KUB).

Before someone without any specific medical knowledge launches an attack along the lines of...'but the asker was not asking about kindney/urether/bladder imaging', please note the following:

In medicine, KUB refers to a diagnostic medical imaging technique of the abdomen. Despite its name, a KUB is NOT typically used to investigate pathology of the kidneys, ureters, or bladder.KUB is typically used to investigate gastrointestinal conditions such as a bowel obstruction and gallstones.