A span is the period of time between two dates or events during which something exists, functions, or happens.

Your concentration span or your attention span is the length of time you are able to concentrate on something or be interested in it.

If something spans a long period of time, it lasts throughout that period of time or relates to that whole period of time.

If something spans a range of things, all those things are included in it.

The span of something that extends or is spread out sideways is the total width of it from one end to the other.

A bridge or other structure that spans something such as a river or a valley stretches right across it.