A zoom lens is simply a lens with a variable focal length. It simply distinguishes it from prime lenses, which have fixed focal lengths.
Prime lenses are an older, simpler technical design, and primes are often smaller, sharper, and cheaper than their zoom counterparts. They also have the largest maximum apertures. A prime with a maximum aperture that's f/2.8 or larger (smaller f-number) is also known as a "fast" prime, because the large max. aperture allows for faster shutter speeds.
The categories by focal length (smallest to largest) are:
ultrawide (~10-20mm)
supertelephoto (~>300mm).
Obviously, the crop factor of the camera has some determination on whether a lens is wide angle or normal, or normal vs. short telephoto, but these are the general definitions.
So, for example, Canon's EF-S 10-22 is an ultrawide zoom. The Distagon 21mm is a wide angle prime. Canon's 70-200 f/4L USM is a telephoto zoom. The EF 400mm f/5.6L USM is a supertelephoto prime.
A macro lens is a lens with the additional capability of being able to focus closely (this is usually done by introducing a floating element--a piece of glass that does NOT rack in and out with focus in unison with the other elements in the lens). The strict definition is a lens that can achieve 1:1 magnification--that is, the image on the sensor/film is the same size as the object itself. Most true macros are prime lenses. And most macros are extremely sharp because of the floating element.
And two more oddball lens types you may bump into:
A fisheye lens is one where the lens does not attempt to draw the light in a rectilinear fashion, but rather a curved one. It has a high amount of distortion, but also brings in a larger field of view than a rectilinear lens with the same focal length.
A tilt-shift lens is one that allows for lens movements, analogous to a view camera bellows, only with less freedom. Shifting is used for perspective correction, and tilt for changing the focus plane and controlling depth of field. These lenses are mainly used for product or architectural photography
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