Illustrations, in general, do depict intended information in visual form.
In the commercial sense, this means illustrations are generally designed for a certain purpose. In contrast to an artwork, illustration is often produced in such manner it’s easy to replicate, while the artwork is considered a unique piece or set of pieces (prints and works that contain multiple parts).
An illustration is a decoration, interpretation or visual explanation of a text, concept or process, designed for integration in published media, such as posters, flyers, magazines, books, teaching materials, animations, video games and films.
Illustrations are often found in books for adults because illustrations can help readers to comprehend ideas which are difficult to explain using only written text. The reason for this is that the human brain is able to perceive visual information more quickly. Moreover, visual representation has greater recall value and is held longer in memory than written text. Illustrations are especially useful in instructional manuals, technical books and medical journals where technical sketches, accurate diagrams and flowcharts are used to convey complex concepts. Accurate visual representation is necessary for conveying messages that cannot be adequately expressed by words alone.