Time

Time is the continuing sequence in which events are ordered as past, present, and future. It allows durations and change to be measured.

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Duration: The amount of time an interval between events lasts. Duration is the measurable span that time assigns between events.
Clock: A device that measures and displays time by counting regular cycles. Clocks convert repeated physical processes into units of elapsed time.
Absolute time: The view that time flows uniformly and independently of events or observers. It contrasts with accounts in which time depends on physical relations.
Arrow of time: The apparent one-way direction of time, marked by irreversible processes. It links temporal direction to the asymmetry of physical change.
Temporal order: The ordering of events as earlier, later, or simultaneous. Time distinguishes the order in which events occur.
Calendar: A system for organizing days and longer periods into a year. Calendars coordinate human activity across recurring and extended periods.
Relational time: The view that time consists in relations among events and changes rather than an independent flow. It denies the independent temporal container assumed by absolute time.
Entropy: A thermodynamic quantity associated with the number of microscopic arrangements compatible with a system's state. Increasing entropy helps explain why many macroscopic processes have a preferred direction.
Change: A difference in the state or properties of something over time. Change is what makes temporal succession observable.
Second: The SI base unit of time, defined using a specified frequency of cesium-133 radiation. The second is the standard unit used to quantify duration.