Foot Traffic
The number of people going into a retail store. Times two.
Foot traffic is usually a good proxy for revenues a given store or mall or shopping zone will garner over a given period. The most famous foot traffic metric is the turnstile number at Disneyland; the volumes of people on a daily basis entering The Magic Kingdom used to be perceived as a leading indicator for where the economy was heading. Then Disney started guarding that metric when it was a whole lot more than just Disneyland. It's not such a Small World after all.
Foot traffic also used to matter a lot in normal brick and mortar retail stores. But today, online sales comprise a meaningful part of many businesses' total sales, so the foot traffic figure is kinda "meh" as a metric. Mehtric, maybe. Something like that.
Keyword: Amazon.