lifetime

Lifetime refers to the duration of existence of something from its origin to its end. In common usage, it often denotes the length of a human life—from birth to death—or the useful life of an object or system from manufacture to failure or obsolescence. In statistics and reliability engineering, lifetime is treated as a random variable describing how long a particular item remains functional or how long a person lives.

Biology: For organisms, lifespan is the actual age at death; life expectancy is the average age at death across a population, influenced by genetics, environment, and healthcare. Maximum lifespan is the longest observed age of individuals of a species.

Physics and engineering: The lifetime of a particle or excited state is the average time before it decays. For devices and components, lifetime or service life is the period during which the item performs within specified limits. The term is often distinguished from half-life (time for quantity to halve). Battery life refers to usable runtime; lifetime warranties cover a product for its entire expected service period.

Measurement and modeling: Lifetime distributions are studied in survival analysis and reliability engineering. Common models include exponential and Weibull distributions; metrics include mean time to failure (MTTF), mean remaining lifetime, and reliability functions.

Usage and context: "Lifetime" appears in everyday speech (e.g., "my lifetime") and in commerce (lifetime warranties, lifetime achievement awards).