One should always store ground coffee in an air-tight container. Air (mainly oxygen) and moisture are the coffee's principle enemies. Also the container should be stored in a dark place as sunlight reduces freshness. While you can place coffee in a fridge, do never freeze ground coffee. There are two key problems here. One, the freezing will damage some of subtle tastes in the coffee and two, when the coffee is taken out the container will sweat, exposing your coffee to moisture. Best is only to buy so much, so it will be consumed within a week or to freshly grind beans according to needs.