United States of America perspective
The President of a corporation typically is the most senior corporate officer (frequently also the Chief Executive Officer). The President typically reports to the board of directors.
The Chairman is called, more formally, the Chairman of the Board. This is the board member who is chosen by the board to run board meetings and lead the board in other ways.
In summary, the President runs the business, and the Chairman runs the board.
Sometimes the President / CEO also is the Chairman.
This blog does not constitute legal advice and does not establish an attorney-client relationship. If you need legal advice, please contact a lawyer directly.