Evolutionism - A General Definition
"Evolutionism" means different things to different people. For example, there are theistic evolutionists and there are atheistic evolutionists. But the basic premise behind the evolutionary world-view is atheistic. Theistic evolutionists are those who have managed to reach a compromise between two very distinct world-views: creationism and evolutionism. Evolutionism, in its purer form, is the idea that this universe is the result of random cosmic accidents. Life arose spontaneously via chance chemical processes, and all life-forms are related and share a common ancestor - from bananas to birds, from fishes to flowers, apes to Adam, etc.
Evolutionism - A Broad Overview
Evolutionism is a world-view, which seeks to explain every aspect of this world in which we live. It encompasses a wide variety of topics, from astronomy to chemistry to biology. At its core, it teaches that there were different stages in the evolution of our universe:
Cosmic-evolution. While the original "Big Bang" Theory is now a dead theory, from its ashes have emerged the "Inflationary Universe Theories" (IUT's). Starting with Alan Guth in the late 1990's (The Inflationary Universe: The Quest for a New Theory of Cosmic Origins), the scientific community has proposed roughly 50 different IUT variants. The general idea remains the same: In the beginning there was nothing. Then a "singularity" suddenly appeared, exploded, and the rest is history.
Stellar-evolution, Chemical-evolution and Planetary-evolution. After the primordial Bang, stars and planets slowly evolved. It's thought that the initial explosion produced hydrogen, helium and possibly lithium. These three elements condensed to form the first stars. That's stellar-evolution. The incredible heat and pressure inside of those early stars acted upon the Hydrogen and Helium, producing many of the chemical elements we observe today. This is chemical-evolution. We've identified 118 chemical elements, from Hydrogen (H) to Ununoctium (Uuo). 90 of the first 92 listed in our Periodic Table of Chemical Elements are thought to occur naturally, with the two exceptions being #43 (Technetium or "Tc") and #61 (Promethium or "Pm"). How did the other 87 get here? Apparently, they were produced inside stars. When these stars died, these chemical elements were released into space. These elements eventually came together via natural forces, condensed and formed planets, more stars, and solar systems like our own. This is stellar and planetary evolution.
Organic-evolution. This is the idea that life spontaneously generated in a "prebiotic soup."
Macro-evolution. This is the widely-held notion that all life is related and has descended from a common ancestor: the birds and the bananas, the fishes and the flowers -- all related. From the goo, through the zoo, to you over millions of years! This is the stage of evolution which Charles Darwin popularized in his classic, Origin of Species, published in 1859. Darwin didn't invent the theory, but he gave it credence by supplying a plausible mechanism: natural selection.
Evolutionism - Micro-evolution
The final phase taught in evolutionism is Micro-evolution. This evolutionary phase is unique in that creationists and evolutionists generally agree on this one. This is the idea that there can be variations within different kinds of animals. There can be tall people, short people, black people, and white people. There are many different shades of skin and many different eye colors, but people are still people. Just because your skin color is different from somebody else's, that doesn't mean you're any less human than they are. No, we're all human; we just express different traits. Human DNA allows for these traits. But variation is thought to be constrained by the genetic code. The code itself allows for variation, but there are genetic boundaries in place to limit them (people don't turn into non-people, and pigs will never fly).