Maslow's hierarchy of needs is a set of human needs originally proposed by Abraham Maslow. According to the theory, the most basic needs are physiological. These physiological needs such as food and shelter must be met before someone can focus on achieving the next level, safety needs. After or above safety needs come a need for love and belonging, then esteem and finally, according to the theory, some people are able to satisfy the need for self-actualization or reaching their full potential.
Wikipedia's article on Maslow's hierarchy of needs