The span of something is the distance it reaches from one end to the other, or the amount of time something lasts. A bridge's span stretches across a river from one bank to the other. The Golden Gate Bridge has a main span of 4,200 feet. Your arm span is the distance from fingertip to fingertip when you stretch your arms wide.

When talking about time, span describes a period or duration. The span of a school day runs from morning bell to dismissal. A butterfly's lifespan might span just a few weeks, while a giant tortoise's life can span over a century. Historians study events across the span of decades or centuries.

The word can also mean to extend across or bridge something. The ancient Romans built aqueducts that spanned valleys to carry water into their cities. A single plank might span a creek, letting you walk across. When you span a topic in an essay, you cover it from beginning to end.

Attention span is how long someone can focus before their mind wanders. Reading a difficult book requires a longer attention span than watching a short video. Your attention span grows stronger with practice, like a muscle.