What is the difference between microevolution and macroevolution?

Answer 1

The only difference is time. So-called "microevolution" means changes within a species, accumulated over a relatively short period of time (geologically speaking). So-called "macroevolution" is the exact same process operating over a much longer time, such that the accumulated changes become significant enough to warrant assignment of a new species name to the resulting form. Some folks claim that "microevolution" occurs (they can't deny this, since we can see it happen within our own lifetime), but that "macroevolution" (resulting in new species) does not occur. This position of course is logically untenable. If something gradually accumulates changes over time, then over great expanses of time it will obviously become very different from what it was before, at which point it is only reasonable to call it something else.
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Answer 2

Microevolution is evolution that can be witnessed over a short period of time. This is usually about the span of a human lifetime, and can sometimes be called adaptation. Macroevolution however is the long term change in traits that leads to the distinction of a brand new species. Contrary to other people's answer, these two evolutions have nothing to do with the size of the animal.

Answer 3

Microevolution is also known as adaptation, or when an animal changes to fit its surroundings, but not in such a way that it becomes a new species.
Macroevolution is the belief that all life forms are descended from one common ancestor, and it is this one that creationists are at odds with.