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 optical zoom, which uses moving lenses for maximum quality. Unlike digital zoom, optical zoom has no trade-offs in quality or image size.
Digital zoom is a software feature that uses one of two methods:
One type of digital zoom simply "crops" the edges of the image. There is no loss in quality, but the resulting image is smaller than the maximum resolution of the camera. The image has the same exact amount of detail as a non-zoomed at full size.
The other type uses software to stretch the cropped image larger. The resulting image is the same size as the maximum resolution, but because it has been stretched, no additional detail is visble, meaning the image appears much blurrier than a non-zoomed photo.
See: Optical Zoom