Maslow's hierarchy of needs is a psychological theory introduced in 1943 that outlines a five-tier model of human motivation, where individuals must satisfy lower-level basic needs before progressing to higher-level growth needs. These needs include physiological, safety, love and belonging, esteem, and self-actualization, with the ultimate goal being personal growth and fulfillment. The order of need fulfillment is flexible, allowing for individual differences and varying life circumstances.