Aging is the process of growing older and the gradual changes that happen to living things over time. Every person, animal, and even plant ages: a puppy becomes an adult dog, then a senior dog with gray fur around its muzzle. A tiny acorn grows into a mighty oak tree, which eventually weakens and falls. Your great-grandmother has aged from the baby her parents once held to the wise, experienced person you know today.

In humans, aging brings both losses and gains. Bodies change: hair turns gray, skin wrinkles, and movements may slow down. But aging also brings wisdom, perspective, and often a deeper understanding of what truly matters. Someone who has lived through many experiences, both joyful and difficult, usually develops judgment and insight that younger people haven't had time to acquire yet.

Scientists study aging to understand why it happens and how to keep people healthy longer. Some materials also age: leather develops a rich patina over decades, while metal might rust. When we talk about aging cheese or aging wine, we mean letting time improve their flavor. The word can be a noun (the aging of the tree), a verb (the tree is aging), or an adjective (an aging athlete still competing at fifty).