The definition of"business" under immigration law is limited, and does not generally allow for gainful employment, labor for hire or productive activity such as operating a business or consultancy work.
Specifically, in the applicable U.S. law the term "business" is limited to
(a) the negotiation of contracts,
(b) consultation with business associates,
(c) litigation, and
(d) participation in scientific, educational, professional or business conventions,conferences or seminars and other legitimate activities of a commercial or professional nature.
What it is NOT.
Persons entering the U.S. on a visitor visa, for business or tourism (B-1/B-2), or without a visa on the Visa Waiver Program are not permitted to work, i.e. being "gainfully employed" in the United States. If you are planning to work, or to attend certain training in the U.S., you cannot enter the U.S. with a visitor visa. Instead, you will need a visa in one of the employment categories for temporary workers.
Examples of Acceptable Activities
The following are some further examples of legitimate B-1 activities:
(1) Attending a scientific, educational,professional or business convention, conference or seminar,
(2) Giving a lecture,
(3) Doing independent research at a scientific or educational institution,
(4) Participating in a voluntary service program,
(5) Participating in a sporting event.
People who have B-1 visas may not, in general, receive salaries or compensation from U.S. sources. You may be able to come to the U.S. on B-1 status whereby you continue to receive your compensation back home, and may only receive expense reimbursements in the U.S., but no direct financial gain.
If a business traveler, or a company for that matter, is in any doubt as to their anticipated or proposed conduct in the United States, DO seek the advice and counsel of a qualified immigration lawyer, BEFORE the business traveler boards that mission-critical flight US-bound.