Am I just supposed to know what "creative coding" is? It is not defined anywhere on the page. What specifically distinguishes "creative coding" from just "coding"?

Creative coding is a type of computer programming in which the goal is to create something expressive instead of something functional.

Wikipedia

I kinda figured this out from context clues, but they really should introduce the term on this page!

Anyone know what "expressive" means here?

Also, you could have provided a link to the wikipedia article this is from.

Art. Creative coding is creating art, be that visual art or music.

Art is always left undefined. This is a feature, not a bug.

Back in 80/90 we used to call it "demoscene".

It's a well established term.