Phase detection is a method used in cameras to quickly and accurately focus on subjects. It works by comparing the phase of light coming from different parts of the lens. When the light waves are in sync, the camera knows the subject is in focus. If they are out of sync, the camera adjusts the lens until they align, achieving sharp focus. This technique is commonly found in DSLR and mirrorless cameras, making it ideal for capturing fast-moving subjects. Phase detection is faster than other focusing methods, such as contrast detection, which relies on analyzing the image for sharpness.