Maslow's hierarchy of needs is a theory that proposes human needs are arranged in a hierarchy. The lowest level needs must be met before higher level needs can be fulfilled. Physiological needs like food, water, shelter are the most basic. Safety needs, social needs, esteem needs, and self-actualization needs are higher level needs that can only be addressed once lower level needs are satisfied. The document provides examples of how advertising targets different levels of needs to sell various products and services.