Perceived self-efficacy refers to beliefs that individuals hold about their capability to carry out action in a way that will influence the events that affect their lives.

Modified definition: Bandura (1994)

Self-efficacy beliefs determine how people feel, think, motivate themselves and behave. This is demonstrated in how much effort people will expend and how long they will persist in the face of obstacles and aversive experiences.

Source: WHO Health Promotion Glossary: new terms. Smith BJ, Tang KC, Nutbeam D. Health Promot Int. 2006 Dec;21(4):340-5.