Questions about methods of combining varying text and fonts with relatively simple illustrations (click to see example); also illustrations used to emphasise a message or content by the use of for example graphs, charts, maps or other visualisations.
Example of humorous information graphic from The Oatmeal 15 things worth knowing about coffee
Please note that illustration is a field on its own. It is often confused with other disciplines most notably that of graphic design and fine art, perhaps because there is sometimes an overlap.
However: illustration is about communicating a specific contextualised message to an audience. It is rooted in an objective need to fulfil a particular task.