What is the difference between declaration and definition?

The declaration tells the compiler that at some later point we plan to present the definition of this declaration.
E.g.:

void stars () //function declaration

The definition contains the actual implementation.
E.g.:

void stars() // function definition
{
    for (int j = 10; j & gt; = 0; j--) //function body
        cout & lt; & lt; * ;
    cout & lt; & lt; & gt;
}