A commerical user is generally understood to be someone for whom the primary use of the software is in the furtherance of generating profit.

This is different from the use of software by not-for-profit organizations or home users. For the latter, there's no money at all. For the former, there is no profit motive.

Please note that these are the understandings (as I know them) in the US. I think the EU and the US generally track together in this, but I'm not positive.