Optical zoom: If taking lots of pictures of distant subjects is important to you, make sure the camera you buy has optical zoom. An optical zoom is a true zoom lens, like the zoom lens you’d use on a film camera. They produce much better quality pictures.
Digital zoom is a method of reducing the exact angle of view of a digital photograph or video image. It is accomplished by cutting an image into a field with the same aspect ratio as the original and by scaling to the original dimensions of the image. Digital Zoom and Optical Zoom
Digital Zoom: Some cameras offer a digital zoom, which is simply some in-camera image processing. When you use a digital zoom, the camera magnifies the image area in the center of the frame and zooms out to the outer edges of the picture. The result is the same as when you open an image in your photo-editing program, awaiting cropping. Digital Zoom and Optical Zoom
Full-size cameras usually have an optical zoom lens, but some automatically apply digital zoom after the optical focal length has been completed for as long as possible. Digital Zoom and Optical Zoom