A [b]fluoroscope[/b] is a type of [[x-ray]] device in which the rays pass through the patient and onto a fluorescent screen, which displays a real-time x-ray image of the patient's body. This is the classic cartoon "character stands behind screen which magically reveals their bones" x-ray device, which is the form in which it's most likely to appear around here, even though the cartoon versions usually omit the actual x-ray source (which must be behind the patient for the fluoroscope to work).

Fluoroscopy was a common technique used in the early scientific investigation of x-rays, as well as their medical employment, before the dangers of continuous x-ray exposure to both patient and physician became better-known.  Modern fluoroscopes with extensive safety mechanisms are still used for some procedures (e.g., lumbar punctures) where their real-time capabilities are valuable, but for most diagnostic purposes, they have long since been supplanted by still-image radiography.
fluoroscope