Live view is a camera mode in which the sensor’s output is displayed in real time on the rear LCD or in an electronic viewfinder, replacing or supplementing the optical viewfinder. On a mirrorless camera, live view is the only mode; the mirror box that would otherwise route light to an OVF does not exist, and the sensor reads continuously to drive the EVF or LCD. On a DSLR, live view is optional and engages by flipping the mirror up to expose the sensor to the lens.
The biggest practical benefit is exposure simulation. Because the displayed image comes from the sensor itself, the live view shows what the file will actually look like at the current settings: how bright, how saturated, how white-balanced. Photographers can adjust shutter, aperture, and ISO and see the change before pressing the shutter button. Manual mode becomes much faster to use because feedback is immediate, which is one of the reasons mirrorless cameras have made manual exposure mainstream again.
Focus aids depend on live view to function. Focus peaking overlays colored highlights on the in-focus edges of the live image; punch-in magnification zooms to 100% or higher to verify sharpness; a focus distance scale displays the actual focused distance. None of these are possible through an OVF because the OVF shows the scene optically rather than as a processed sensor stream.
On DSLRs, live view also enables contrast-detect autofocus and, on later bodies, on-sensor phase detection via dual-pixel architectures. Through the optical viewfinder, DSLRs use a separate dedicated phase-detect module that is faster but less accurate and less flexible. Studio and landscape photographers often shoot a DSLR exclusively in live view to get more precise focus and a wider AF point coverage, even though the body still has an optical finder available.
Drawbacks are real. Live view drains battery faster than an OVF because the sensor and the screen are both active. It can lag in very low light as the camera struggles to refresh the display, a problem mostly solved on recent bodies but still noticeable in budget gear. It also introduces some EVF lag on mirrorless bodies, where the displayed image is a few milliseconds behind reality, an issue for fast-moving subjects like birds and sports.
Tethered, studio, and video workflows all rely on live view. Tethering software like Capture One displays the live feed on a laptop or tablet, letting the photographer and an art director see the framing and exposure before committing. Video recording obviously requires continuous sensor readout. Astrophotographers use live view at maximum gain to compose on impossibly dim scenes. The mode has gone from a niche feature on early DSLRs (the Olympus E-330 was the first, in 2006) to the default mode of every modern camera.