Eternity is time that never ends, or a period so long it feels endless. When religious texts describe heaven lasting for all eternity, they mean it goes on forever, without any end point you could mark on a calendar. Mathematicians use the symbol ∞ (infinity) to represent the idea of something without limits.

People also use eternity to describe something that just feels incredibly long. When you're waiting for your birthday to arrive, those final few days might seem like an eternity. When you're sitting in the principal's office waiting to explain what happened at recess, those minutes can feel eternal. A boring lecture might feel like it's taking an eternity to finish, even though it's really just an hour.

Throughout history, humans have wondered about eternity: what it would be like to live forever, whether the universe itself is eternal, or how to create something that lasts. The ancient Egyptians built pyramids designed to stand for eternity. Writers hope their books will achieve eternal fame.

When someone says “I'll love you for eternity” or “I'll remember this forever,” they're using the word to express something so powerful that ordinary time limits don't seem big enough to contain it.