"Self-esteem" is simply a psychological term used in reference to one's image of oneself. In other words, how much self-respect an individual possesses is a measure of self-esteem.
While the concept of self-esteem is certainly nothing new -- in fact, it was studied as far back as the 19th Century -- its focus in psychological terms is relatively recent. The term "self-esteem" was first used by William James, a psychologist who wrote in 1892 about the effects of negative self-images among children.
The 1950s and 1960s were an important decade in the study of human emotions and one of the leading students of psychology was Nathaniel Branden, who is credited with the modern development of theory on "self-esteem. As, arguably, one of the fathers of the study of "self-esteem," it is only reasonable to quote Branden on its definition:
"Self-esteem is the disposition to experience oneself as being competent to cope with the basic challenges of life and of being worthy of happiness. In is confidence in the efficacy of our mind, in our ability to think. By extension, it is confidence in our ability to learn, make appropriate choices and decisions, and respond effectively to change. It is also the experience that success, achievement, fulfillment -- happiness -- are right and natural for us."
As Branden notes, those with "high self-esteem" are those for whom success in life is expected and its attainment part of a natural progression. Individuals with high self-esteem believe they can achieve their goals, and that they are worthy of a good life. As such, they project positive images of themselves onto others. Conversely, individuals with low self-esteem believe they are destined to fail, and are not worthy of happiness and success. They project negativity and are often depressed, or at least have grown accustomed to having low expectations of life.
Up to the 1960s, the study of "self-esteem" concentrated primarily on the emotional development of children, and it continued to place much of its emphasis on children. During the 1960s and 1970s, the interest in self-esteem began to merge with the growing role of feminism. As women began to question their "traditional" role in conservative cultures, they began to think, often with the help of therapists trained in the study of self-esteem, of the cultural obstacles they faced to self-fullment. Many women began to believe that these cultural inhibitions precluded them from achieving all that they were capable of, and of living more full lives. Many suffered from low self-esteem -- the belief that they didn't deserve more out of life because society had preordained that they be limited in their expectations.
Despite the convergence of feminism and self-esteem, however, the preponderance of scientific study continues to reside with the emotional development of children.