Zoom is a feature of many cameras and camera phones that makes the subject appear "closer", filling more of the image area.
The other type of zoom is digital zoom, a software feature that has trade-offs in image size or quality. Many cameras and some camera phones offer both optical and digital zoom, for increased total zoom.
Optical zoom uses moving lenses to make the subject appear closer. Unlike digital zoom, additional detail is visible when optical zoom is used.
See: Digital Zoom