In this context it seems to refer to programming in a language where the developer facing code is represented in terms of data structure literals within the language. It's a reasonable understanding of what is usually meant in a Lisp-like setting. The code is a list, so you can trivially construct and deconstruct executable lists, just like you can trivially construct data carrying lists.
One could make clever quips that this isn't enough, you need quote/unquote as well to make it practical, and is that really implied by homoiconicity? Should we really use this word? Maybe we should pay someone to make up a new one?