Focal length is a crucial aspect of photography that determines the magnification and field of view in captured images. It is the distance between the lens's optical center and the camera's image sensor when the subject is in focus. A shorter focal length results in a wider angle of view, making it suitable for landscape and interior shots. In contrast, a longer focal length provides greater magnification, ideal for portrait and wildlife photography. Understanding focal length helps photographers select the right lens for different shooting scenarios.