What does “const class” mean?

The const is meaningless in that example, and your compiler should give you an error, but if you use it to declare variables of that class between the closing } and the ;, then that defines those instances as const, e.g.:

const class A
{
public:
    int x, y;
}  anInstance = {3, 4};

// The above is equivalent to:
const A anInstance = {3, 4};