1 : a plan that allows employees to contribute to an investment pool managed the employer
2 : a long-term outline of a project or government function; "the zoning board adopted a master plan for the new development"
3 : an organized plan for employees of a company to buy shares of its stock
4 : a plan for actively doing something
5 : an imaginary line around the Earth forming the great circle that is equidistant from the north and south poles; "the equator is the boundary between the northern and southern hemispheres"