Chocolate Wafer Crust

From the Better Homes and Gardens Cook Book

1 1/2 c finely crushed chocolate wafers (about 25 wafers)
6 tablespoons butter or margarine, melted.

In a mixing bowl combine crushed wafers and the melted butter or margarine; toss to thoroughly combine. Turn the chocolate crumb mixture into a 9-inch pie plate. Spread the crumb mixture evenly into the pie plate. Press onto bottom and sides to form a firm, even crust. Chill about 1 hour or till firm.

I have a recipe that calls for this kind of crust. I have but one question. What are chocolate wafers?