A class is an abstract data type equipped with a possibly partial implementation. An object is an instance of a class. The software text that serve to produce systems are classes.
Objects are a run-time notion only.
The class is a software text. It is static, it exists independent of any execution. In non-OO distinct concepts Class is both a module, unit of software decomposition, but also a type. Uniform Type System. OO provides a simple uniform framework basic types are classes also and can partake in all OO games.