C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 7:
7.1 What is a class?
7.2 What is an object?
7.3 When is an interface "good"?
7.4 What is encapsulation?
7.5 How does C++ help with the tradeoff of safety vs. usability?
7.6 How can I prevent other programmers from violating encapsulation by seeing the private parts of my class?
7.7 Can a method directly access the non-public members of another instance of its class?
7.8 Is Encapsulation a Security device?
7.9 What's the difference between the keywords struct and class?
[7.2] What is an object?

A region of storage with associated semantics.

After the declaration int i; we say that "i is an object of type int." In OO/C++, "object" usually means "an instance of a class." Thus a class defines the behavior of possibly many objects (instances).