Hi there,
@WFab pretty much nailed it. “Commercial use”, as defined by World Machine, is using the assets output from World Machine in any way that makes you (or someone else) money. So for example, building a landscape for a game, or creating landscapes to sell in an asset store are both approved commercial use. The license is with the purchaser specifically and can be used across many projects.
Both the Indie and Professional licenses allow commercial use. There are no limitations on the Indie license in terms of what you can do with the output; there are simply features that the Pro version has that the Indie version does not include.
The only major prohibition of a license is that you cannot share your license with anyone else. Each licensed copy of World Machine must be run by only a single user at a time.
Hope that helps!