Most Replenished refers to the with the highest replenishment rate. Opposite to Least Replenished, when you sort by Most Replenished, the list of products shown will be ordered from left to right starting with the with the highest replenishment rate. This can act as an indicator that the SKUs shown first are in demand for a brand/retailer in the market.
Aside from identifying popular products, the Most Replenished sorting function can also be used to identify a core or basic products of a brand or retailer. You can do this by first sorting by Most Replenished and then looking into the date the SKUs are launched.