Self-efficacy is the extent or strength of one's belief in one's own ability to complete tasks and reach goals.This can be seen as the ability to persist and a person's ability to succeed with a task.Self-efficacy affects every area of human endeavor. By determining the beliefs a person holds regarding his power to affect situations, it strongly influences both the power a person has to face challenges competently and the choices a person is most likely to make.

I think it is more than 50 words....
But hope would be helpful.... : )