Maslow's hierarchy of needs is a motivational theory comprising five tiers of human needs arranged in a pyramid structure. The lowest tier includes physiological needs like food, water, warmth and sleep. The next tier is safety needs, followed by love and belongingness. Esteem needs make up the fourth tier, and self-actualization needs are at the top tier. Maslow theorized that people are motivated to fulfill lower level needs before progressing on to meet higher level needs.