Phase detection is a method used in cameras to quickly and accurately focus on subjects. It works by comparing the light coming from different parts of the lens. When the camera detects a difference in phase, it adjusts the lens until the light aligns, achieving sharp focus. This technique is commonly found in DSLR cameras and some mirrorless cameras. It is faster than other focusing methods, like contrast detection, making it ideal for capturing moving subjects. Phase detection is essential for photographers who need reliable and swift autofocus in various shooting conditions.