Business requires legal formalities for running. A professional is when someone is an expert in a field and is a member of a professional body. Employment happens in a company where a person is employed for doing a specific job. A business involves buying and selling of goods and service.
A profession involves giving expert advises and an employment is working under service contract. Business incurs profit, but a professional gets fee for his profession. For setting up a business, capital requirement is there.
Whereas, for a profession there is little requirement and for employment there is none. Business has a lot of risk and uncertainties. On the other hand for profession, fee is fixed hence low risk and for employment, there is no risks involved.