A module is a set of one or more contiguous program statements having a name by which other parts of the system can invoke it, and preferably having its own distinct set of variable names. In other words, a module consists of a single block of code that can be invoked in the way that a procedure, function, or method is invoked. (Stevens, Myers and Constantine)
A more general definition of module is as follows:
A module is a lexically contiguous sequence of program statements, bounded by boundary elements, having an aggregate identifier."
Procedures and functions are modules. An object is a module, and so is a method within an object.