what is illustration?

This illustration was created by Aleksei Bitskoff for BookTrust, a British charity that focuses on literacy. It looks to be digitally painted to inspire young people to read more, as well as to support books in general and the thoughts they inspire. Bitskoff lives and works on storybook illustrations in London, but he grew up in Estonia studying language intending to be an English teacher.
I chose this particular piece because to me this is one of the clearest examples of what illustration is and what it's meant to do for us. It's meant to captivate, to inspire, to involve us in the picture and make us curious about the source. It's not meant to give us a message, it's meant to tell us about it. You don't need words or fancy details to tell how much fun the little girl's having with her book and imagination because you can see it even in the blank spaces.