What does evolution mean in biology?

The term evolution in biology refers to change over time. It also means descent with modification. This is a term that was used by Charles Darwin (1809–1882) that means species are descendants of earlier ancestral species that are different than the ones that exist in the present time. It can refer to the change that occurs over time in the genetic composition of a species. Darwin felt that new species arose over time, as organisms inherited characteristics that enhanced their ability to survive and reproduce in a specific environment. This led to the idea of natural selection and later the book, The Origin of Species. Some important observations and inferences Darwin wrote about is that members of a given population often vary in their inherited traits. Next, living things can produce more offspring than the environment can support. These observations led to the following inferences: individuals whose traits give them an ability to better survive and reproduce in an environment tend to leave behind more offspring than those less adapted. Another inference was that this unequal ability to successfully survive and reproduce would leave behind offspring with an accumulation of more "favorable traits" in this given environment. Darwin thought that due to natural selection, species would be modified according to their environment over time; this would eventually lead to new species developing. I have attached a link to an interesting summary of some of Darwin's ideas.