illustration Definition

1. A picture or diagram that is used for clarifying or decorating a text, book, lecture, etc.

Thesaurus: picture, engraving, etching, cartoon, frontispiece, vignette.
2. An example.

Example: The essay was an illustration of her brilliance
Thesaurus: example, sample, model, instance.
3. The act or process of illustrating or the state of being illustrated.