For the purpose of the Visa Waiver Program, "business" generally refers to business activities other than the performance of skilled or unskilled labor. Examples of activities that are allowed include: engaging in international commercial transactions, which do not involve gainful employment in the United States (such as a merchant who takes orders in the U.S. for goods manufactured abroad, or who travels to the U.S. to purchase American-made goods for export from the U.S.); negotiating contracts; consulting with business associates; and participating in scientific, educational, professional or business conventions, conferences, or seminars.
The performance of any skilled or unskilled labor - even if it is unpaid - is most always prohibited. This includes performing work in the U.S. as a trainer or consultant. Activities allowed on the VWP parallel those activities allowed with a standard "B1" category business visa. Please see our B visa information page for more details.
Working visas are, as stated, not exactly trivial to get. (And if you're already at the airport it is too late.)