Speciation refers to events or processes leading to the creation of new species.
Biologists generally believe this occurs when a parent species splits into two populations, perhaps separated by geography, each of which then accumulates changes from sexual reproduction and random mutation until the two populations are no longer capable of interbreeding. Among lower forms of life such as bacteria, single mutations can cause drastic changes (called "saltation") that can result in speciation in a very short time.
The exact mechanism of this process is the subject of some debate. Some biologists, such as Stephen Jay Gould, have argued that species usually remain static over long stretches of time, with speciation occuring rapidly in a process called Punctuated Equilibrium. Others have argued that speciation is more often the gradual accumulation of incremental changes over time. It is, of course, entirely possible that both mechanisms operate simultaneously on different species.
Most creationists reject the scientific view of speciation.
See: theory of evolution