Holey Cheese is a type of cheese that is characterized by its holes, or 'eyes'. It is made from cow's milk and is usually aged for several months. The two most popular types of holey cheese are Gruyere and SWISS. Gruyere is a hard yellow cheese with a nutty flavor, originating from Switzerland. SWISS cheese is a mild-flavored cheese with large holes, originating from Switzerland as well. Both Gruyere and SWISS are popularly used in fondue and other dishes.