Washing soda is often confused with baking soda but it's quite different. For starters, you don't bake with it! It's not edible. It is great as a laundry additive, to boost the cleaning of your detergent.
You can make an effective scouring powder out of washing soda and baking soda. Mix 1/4 cup washing soda with 1 cup baking soda and use it as you would Comet or Ajax scouring powder. Washing soda can be purchased in the laundry aisle of your local grocery store.
This is a page about buying washing soda. Washing soda is primarily used for cleaning laundry but it can be used for other cleaning tasks around the house.