To see the product click on Meringue Powder link on recipe above (at ingredients section).
Here is a description of Meringue Powder taken from a Wilton Product:

“Meringue Powder is a pasteurized egg product used for royal icing, meringue and boiled icing. Royal icing is used to make flowers and decorations that can last for months without softening. Snow White Buttercream Icing is also made with Meringue Powder. Flowers can be air dried.” (C)Wilton

Overall, meringue powder is a mixture of dried egg whites, sugar, gum, corn starch and some stabilizers. This powder is very convenient to use and it is usually called for in a recipe for the increasing fear of raw eggs. Eggs are pasteurized in the meringue powder. This can be substituted by making a soft meringue and using it instead of the meringue powder in the recipe. Soft Meringue Recipe- beat 3 egg whites at room temperature (copper bowl works best, if not, second option is glass bowl – do not use aluminum bowl or plastic as aluminum reacts with eggs and makes them gray and plastic usually has traces of oil from previous uses). First begin slowly until some bubbles form. Add 1/4 teaspoon cream of tartar and a pinch of salt, continue beating. Increase speed until soft peaks form. Add 2/3 cups of superfine sugar gradually and continue beating until you get stiff peaks (apx 10 mins). This makes about 4 cups of soft meringue.