Evolution is a process of change over time. Generally the term evolution is used and understood as part of the Darwinian theory of evolution in which species are believed to have changed over time as a means of adapting to changes in the environment. Natural selection is also a component of evolution in which species develop helpful natural mutations that allow members of a species to reproduce more successfully which ensures more of their genes are passed down to future generations.
Evolution can also be used in a descriptive sense to describe any positive, ongoing, change in people, places or circumstances. For instance, over time a situation can "evolve" from seeming hopeless to becoming positive (such as a formerly homeless person might find work, a place to live, and hope for the future).