What term describes the distance from a lens to its focus?

The term that describes the distance from a lens to its focus is known as the focal length. This is a fundamental concept in optics, specifically when dealing with lenses. The focal length is the distance measured from the lens's surface to the focal point, where parallel rays of light either converge (for a converging lens) or appear to diverge from (for a diverging lens) after passing through the lens.

The focal length is crucial for determining how a lens will bend light and is central to applications in photography, vision correction, and various optical instruments. It directly influences the size and position of the image formed by the lens, making it a key parameter in understanding lens behavior.

Understanding the focal length helps in grasping concepts like magnification and the nature of the images (real or virtual) formed by different types of lenses.