A lifespan is the length of time that a living thing exists from birth to death. Every creature has a typical lifespan: mayflies live for just one day, while giant tortoises can live for over 150 years. Humans in modern times often live into their seventies, eighties, or beyond, though this varies depending on many factors, including healthcare, lifestyle, and genetics.

The word can also describe how long non-living things last. A car's lifespan might be 15 years before it wears out. A smartphone's lifespan is usually just a few years before it becomes outdated or stops working well. Buildings can have lifespans of centuries.

Scientists study lifespans to understand why some species live longer than others. Smaller animals like mice typically have shorter lifespans than larger animals like elephants, though there are fascinating exceptions. Ocean quahogs, a type of clam, can live for over 500 years.

When people talk about extending the human lifespan, they mean finding ways to help people live longer, healthier lives. Lifespan measures the total duration of life: a mayfly's single day is a complete life for that insect, filled with everything it needs to do. Understanding lifespan helps us appreciate both the brevity and the wonder of life in all its forms.