The term evolution first came to prominence when Charles Darwin used it in his book The Origin of Species. He showed that minute changes to an organism that make it better adapted to its environment increases the likelihood of the organism living to have offspring with the same adaptation. Strictly this adaptation process occurs at the gene level. Put bluntly, the ones that do not adapt die off. Over vast periods of time all sorts of improbable animals and plants can develop, all the way from peacocks to Venus fly traps.
Now the term is used in other fields:
In stars, nuclear fusion creates many different elements from a ball of Hydrogen gas.
Classic Darwinian plant and animal evolution.
Ideas pass from human to human via air, pages, and h2g2, and are developed by thinking about them.