Pound is a railroad term that indicates the weight of rail per yard. For example one yard of "132 pound rail" weighs 132 pounds. Sizes under 100 pound rail are usually for lighter duty freight, low use trackage, or light rail. Track using 100 to 120 pound rail is for lower speed freight branch lines or rapid transit (for example, most of the New York City Subway system track is constructed with 100 pound rail). Main line track is usually built with 130 pound rail or heavier.
