We live in a world built on tiny details. Some of like to capture this details in photos for pleasure or for practical purposes, or both. It makes sense to photograph your jewellery or coin collection for insurance records. A large of number of stock photographs are taken at a macro level, using every day objects to create memorable illustrations used in magazines or on websites.
For great examples of macro photographs, visit the Closer and Closer group on Flickr.
The term macro is not rigidly defined. Traditionally macro lenses were defined by their level of magnification relative to the size of the 'film plane', that is the size of the negative or now the digial sensor. The ideal was regarded as 1:1, where the camera was capable of focusing on a subject so close to the lens that it was life-size on the film plan.
A good way of describing this is to think of large postage stamp, which is typically a similar size to a 35mm negative. A macro lens with 1:1 capability can focus on the stamp at a point where the image fills the entire view-finder, meaning it fills the negative or the digial sensor. When the negative is processed and turned into a 6"x4" print, the stamp will be massively magnified.
In recent years the term macro has come to mean the capability to focus on a subject close enough to appear life-size on a standard sized print. In real terms this represents a magnification level of only 1:4, which is much less than 1:1.
There's an incredible fascination with seeing the world through pictures captured with a macro lens. Tiny details erupt into view, almost invisible to the naked eye but exposed by the magnifying capabilities of the macro lens. For the newcomer it's a whole new realm of photographic opportunities.