IHOP is short for International House of Pancakes. They are famous dependable for a never-ending pot of coffee, a variety of syrup flavors at each table, and for being Lewis Black's favorite "health club". The pancakes are good, but their sandwiches, burgers, and entree's are average, sometimes very greasy. The menu has some variety, so there's something for everyone anytime of day. In the larger cities, there's at least one that's open 24 hours a day.
Like most chain restaurants, the service and quality vary from place to place; paradoxically, I've noticed that the busier the IHOP is, the better the quality of food and cleanliness at that time. My local IHOP usually isn't all that busy (they're a 7am to 11pm shop), but I like the fact it's dead quiet if I'm hungry at 8pm at night, if nothing else.