In general, evolution simply means "change".
In biology, there were two competing theories of evolution for a while, Lamarckian evolution and Darwinian evolution. Darwinian evolution held that populations of organisms become adapted to their environment due to differences in rates of survival and replication. Lamarckian evolution is different. For example, Lamarck's theory held that "The giraffe evolved a long neck because giraffes had to stretch their necks to reach the high branches, and they passed on their stretched necks to their children, who did the same." Both theories agreed that it takes many generations for biological evolution to take place, but they disagreed on the specifics of how that evolution occurs.
Eventually, Darwinian evolution was found to be consistent with the results of experiments while Lamarckian evolution was found to be inconsistent. So these days, the word "evolution" is generally taken to mean "Darwinian evolution", also known as "evolution by natural selection."
However, we're currently in the midst of a revolution in biology. It turns out Lamarckian evolution does occur in certain species under certain circumstances. So there are definitely two kinds of evolution going on. I would argue that Darwinian evolution is more fundamental, and that Lamarckian evolution probably arose as a Darwinian adaptation, however that's up for debate.