Self-esteem: An assessment of yourself that consists of believing you are competent to live your life and worthy of living it.
Proper self-esteem means having the abilities needed to live a healthy life, and being a good person. The self-esteem is an assessment of these facts, and the emotional results of such an assessment. When you feel that you are competent to deal with the world, you come from a solid base to explore new things, take risks, and venture into the unknown. You have the confidence to use your skills and the knowledge that you can rely on yourself.
Unfortunately, many modern uses of self-esteem emphasize liking yourself without rooting that emotion in an objective assessment. You're supposed to feel good about yourself, whether you deserve it or not. One justification says that a high self-esteem gives people the confidence to try new things. But when your assessment is not grounded in fact, it's quite fragile. You may feel good while people praise you, but there's no substance behind it. The first insult or failure will shatter that illusion.