Eternity refers to something that has no beginning or end, existing forever beyond the limits of time. It is often used in philosophy, religion, spirituality, and literature to describe:

Infinite time or endless duration
A state outside normal human experience of past, present, and future
Immortality or everlasting existence
The universe, soul, or divine beings in many belief systems

In everyday language, “eternity” can also describe something that feels extremely long, such as waiting “for an eternity.”