A theory is a testable statement in science that takes concepts, definitions, and assumptions and combines them to provide a predictive view of an observable fact or an event. Nursing theories define and explain nursing care, guide nursing practice, and serve as a basis for clinical decision-making. There are four metaparadigms that serve as essential foci of nursing theories: person, environment, health, and nursing. These four interrelated concepts serve as an umbrella for the outlook that describes nursing practice. A "person" refers to the recipient of nursing care and includes individual patients, families, groups, and communities. Health corresponds to a person's position on the health-illness continuum. Individuals define their health based on their values, lifestyles, and personality. The meaning of health varies depending on the individual patient, the clinical setting, and the healthcare profession. The environment includes a patient's surroundings that can influence their health and wellness, such as physical, occupational, and environmental factors. The nursing component refers to nurses' attributes and their application of knowledge and skills during patient care.