Final answer:
Stress is the physiological and psychological response to a challenging or threatening condition that requires adaptation. Chronic stress can lead to health issues such as immune dysfunction and heart disease.
Step-by-step explanation:
The physiological and psychological response to a condition that threatens or challenges a person and requires some form of adaptation or adjustment defines stress. Stress responses can include physiological changes such as increased heart rate and psychological adaptations necessary for coping with perceived threats. Stress can be conceptualized as both a challenge and a threat, depending on the individual's appraisal of the situation and their ability to cope. Over time, chronic stress can result in health issues like impaired immune system function and an increased risk of cardiovascular diseases.