Illustration has two main meanings:
1. A visual representation that helps explain or clarify something. This could be a drawing, painting, photograph, diagram, or even a short video.
2. The act of creating a visual representation to explain something. This is often done by an artist or designer.
For example, a textbook might use illustrations to show how the human body works, or a website might use illustrations to explain a complex process.
If you're referring to a specific context where "illastration" was used, please provide more details and I can give a more accurate answer.