OK zoom refers to a focal length that can change.
For more on focal length, refer to wikipedia:
http://en.wikipedia.org/wiki/Focal_length Scroll down to the bit about photography.
You can have a wideangle lens, which makes things look smaller than the eye perceives them, a normal lens (50mm on a full-frame camera) that makes things about the same size as what we see and a telephoto lens which makes them look bigger.
A lens that can change focal lengths (as opposed to one where the focal length is always the same, or a prime lens) is called a zoom lens.
Focussing down to very small distances, taking pictures of very small things is called macro photography.