Full frame describes a sensor measuring approximately 36x24mm, matching the size of a single frame of 35mm motion picture film as adapted for still cameras by Oskar Barnack at Leica in 1913. It is the reference standard against which other formats are described, and the size most modern lens designs target. Full frame sits larger than APS-C (roughly 24x16mm) and Micro Four Thirds (17.3x13mm), and smaller than the medium-format sensors used by Hasselblad, Fujifilm GFX, and Phase One.
Focal length figures quoted in photography are calibrated to this format. A 50mm lens is normal on full frame because its angle of view roughly matches human central vision when projected onto a 36x24mm rectangle. On a smaller sensor, the same lens captures only the central portion of its image circle, which is why a crop factor is applied. An APS-C body with a 1.5x crop factor sees a 50mm lens as the equivalent of a 75mm on full frame.
The practical advantages of a full-frame sensor stem from its larger surface area. Photosites can be physically bigger at the same pixel count, which improves signal-to-noise ratio at high ISOs and widens the dynamic range. The lens-and-sensor combination yields shallower depth of field at a given framing and aperture, because the larger format requires a longer focal length or closer working distance to fill the frame. That is why full-frame portraits at f/1.8 produce more aggressive subject separation than the same aperture on a smaller sensor.
Tradeoffs run in the other direction. Full-frame bodies and lenses are larger and heavier than their crop counterparts, and price climbs steeply. A full-frame mirrorless system with two professional zooms can weigh several kilograms, while a Micro Four Thirds setup of comparable focal range fits in a small shoulder bag. Telephoto reach also costs more on full frame, since a 400mm lens covers the same field of view that a 200mm covers on Micro Four Thirds.
The first digital cameras to reach full-frame coverage were the Contax N Digital in 2002 and the Canon EOS-1Ds in 2002, both still rare and expensive at launch. Through the 2000s, full-frame was a professional-only tier; bodies like the Canon 5D in 2005 and the Nikon D700 in 2008 brought it into enthusiast hands. By the late 2010s, mirrorless systems from Sony, Nikon, Canon, and Panasonic made it the dominant format above the entry level.
Full frame is not automatically the right choice for every photographer. Crop-sensor systems can match or exceed it in autofocus, burst speed, and weight, and medium format outresolves it in studio and landscape work. What full frame offers is the default reference: lens designs, focal-length intuition, and depth-of-field calculations all assume it unless stated otherwise.