liveness

Liveness refers to the quality of being alive or the capacity for activity in real time. In everyday use it describes organisms or systems that are alive or are operating and capable of change. It is often contrasted with non-life, inactivity, or dead states.

In biology and medicine, liveness denotes life processes such as metabolism, growth, and reproduction. Viability tests assess whether cells, tissues, or organisms are alive and capable of developing under given conditions. Liveness can be affected by environmental stress, disease, or injury.

In computer science, liveness is a property of systems and algorithms meaning that something desirable will eventually occur, assuming fair conditions. A liveness property guarantees progress, for example that every request will eventually receive a response, or that a process will eventually reach a final state. This is contrasted with safety properties, which prohibit bad things from happening but do not guarantee progress.

In distributed and real-time systems, liveness often requires fairness assumptions and progress guarantees under specified scheduling or timing constraints. Liveness analyses help verify that systems do not get stuck in deadlock or livelock.

In the arts and broadcasting, liveness refers to events presented in real time, such as live performances, broadcasts, or streams, as opposed to pre-recorded material. Liveness can foster immediacy and audience interaction but may introduce unpredictability.

Etymology and usage: derived from life, via Old English. The term appears across disciplines with domain-specific meanings but shared sense of 'being alive or active now' within the system described.