Yes, span is a word. It can be used as a noun or a verb. As a noun, it refers to the interval, space, or distance between two points, such as the ends of a bridge or arch, the complete duration or extent, or the amount of material that can be processed in a single mental act. As a verb, it means to measure by or as if by the hand with fingers and thumb extended, to extend across, or to form an arch over. ^{wordreference.com 1 2}