What is the difference between a committee and a board of directors?

Committee is for a specific purpose and stands disolved after the completion of that purpose/goal or objective. For example the reception committe at a gala or function. Whereas the board is of a more permanent nature and functions for a much longer period of time and is hence contituted for projects which have a much longer duration or are ongoing in nature. For example the wages board or the board of a school etc.