A function model represents the model of a Ceylon function that you can invoke and inspect.

A method is a member function: it is declared on classes or interfaces.

This is both a FunctionModel and a Member: you can invoke it with an instance value to bind it to that instance and obtain a Function:

class Outer(){
    shared String foo(String name) => "Hello "+name;
}

void test(){
    Method<Outer,String,[String]> method = `Outer.foo`;
    // Bind it to an instance value
    Function<String,[String]> f = method(Outer());
    // This will print: Hello Stef
    print(f("Stef"));
}