The article defines it through an example:

> You've been wanting to take cooking classes, but you've also been wanting to join an improv group. If you don't have time/resources for both of these projects, you might choose a metaproject like "weekly dinner party with funny friends" -- it doesn't strictly meet the requirements from either project, but it might fulfill some deeper desire.

So the idea is to extrapolate a new project that satisfies some core aspects of multiple projects you dont have time for.

That example was not there when he wrote the comment :) I snuck it in after all the helpful feedback in this comment section haha