A shutter placed just in front of the film or sensor, close to the focal plane. It has two curtains. The first curtain opens to start the exposure and the second curtain closes to end it. At slower speeds, the first curtain opens fully before the second one follows, so the whole frame is exposed at once. At fast speeds, the second curtain starts before the first one finishes, and only a narrow slit between them moves across the frame.
The fastest speed at which the whole frame is open at once is the flash sync speed. Most DSLRs and mirrorless cameras use this type of shutter.
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