An object is an instance of a class. The relationship is such that many objects can be created using one class. Each object has its own data but its underlying structure (i.e., the type of data it stores, its behaviors) are defined by the class.
Many objects can be created from a book class:
Book HitchHiker = new Book("The HitchHiker's Guide to the Galaxy", "Douglas Adams", "William Heinemann"); Book ShortHistory = new Book("A Short History of Nearly Everything", "Bill Bryson", "Black Swan"); Book IceStation = new Book("Ice Station Zebra", "Alistair MacLean", "Collins");