Time is a fundamental concept used to describe the sequence of events that occur in the universe. It is a dimension in which events occur in a particular order, and it is often measured in terms of duration, or the amount of time that passes between two events. Time is usually defined in relation to the motion of objects or the changes that occur in the natural world, such as the rotation of the Earth or the decay of radioactive elements.

In physics, time is considered to be one of the four fundamental dimensions of space-time, along with length, width, and height. The concept of time is also essential in fields such as philosophy, psychology, and sociology, as it is intimately connected to human experience and the perception of causality and continuity in the world.