helicopter parent: The label used for parents who hover (like a helicopter) over their emerging adult children.

intimacy versus isolation: The sixth of Erikson’s eight stages of development. Adults seek someone with whom to share their lives in an enduring and self-sacrificing commitment. Without such commitment, they risk profound loneliness and isolation.

homeostasis: The adjustment of all the body’s systems to keep physiological functions in a state of equilibrium, moment by moment. As the body ages, it takes longer for these homeostatic adjustments to occur, so it becomes harder for older bodies to adapt to stress.

massive open online courses (MOOCs): College courses that are offered solely online. Typically, thousands of students enroll.

organ reserve: The extra capacity built into each organ, such as the heart and lungs, that allows a person to cope with extraordinary demands and to withstand organ strain.

hookup: A sexual encounter between two people who are not in a romantic relationship. Neither intimacy nor commitment is expected.

postformal thought: A proposed adult stage of cognitive development. Postformal is more practical, flexible, and dialectical (i.e., more capable of combining contradictory elements into a comprehensive whole) than earlier cognition.

allostasis: A dynamic body adjustment, related to homeostasis, that over time affects overall physiology. The main difference is that while homeostasis requires an immediate response, allostasis requires longer-term adjustment.

extreme sports: Forms of recreation that include apparent risk of injury or death and are attractive and thrilling as a result.

linked lives: When the success, health, and well-being of each family member are connected to those of other members.

cohabitation: An arrangement in which a couple live together in a committed romantic relationship but are not married.

stereotype threat: The thought that one’s appearance or behavior might confirm another person’s oversimplified, prejudiced attitudes, a thought that causes anxiety even when the stereotype is not held by other people.

allostatic load: The stresses of basic body systems that combine to limit overall functioning. Higher allostatic load makes a person more vulnerable to illness.

emerging adulthood: The period of life between the ages of 18 and 25. Emerging adulthood is now widely thought of as a separate developmental stage.

drug abuse: The ingestion of a drug to the extent that it impairs the user’s biological or psychological well-being.