the terms may vary between countries, but in Australia, the first two have defined meanings. I a public company (a company that is listed on the stock exchange) the Chairman is the person in charge of the Board of Directors. The directors give the company the direction that they want is to follow, but are not involved in the everyday decisions on the companies management (although they usually appoint the senior managers) The Managing Director is appointed by Board of Directors to run the everyday affairs of the company, and to implement the Board of Directors decisions. Often the Managing Director can be a member of the board, but I don't think it is necessary. I think larger companies the positions are kept seperate. 'The big boss' is a slang term, refering to the person who everyone regards as in charge of the company. in a small company, that would be the company owner, but in a large company, that be most likely be the Managing Director. If it is a very big company with many offices, the the big boss may be the person who manages the office that people work at.