Medium Format
Any format larger than 35 mm but smaller than 4×5 inches, covering film frames from 6×4.5 to 6×17 cm and digital sensors around 44×33 mm.
Measured in
mm
In depth
The appeal is tonal: a larger area means shallower depth of field at the same framing, gentler tonal transitions and less enlargement for a given print size. Digital medium format is usually 44×33 mm — about 1.7 times full-frame area rather than the four-fold jump film users remember, so the difference is real but smaller than the name suggests.
Examples in practice
A 6×7 cm negative has almost five times the area of a 35 mm frame, which is why its enlargements hold such smooth gradation.