What is a ferromagnetic substance? What is a magnetic domain?

(N/A) ferromagnetic substance is a material that exhibits strong magnetism in the presence of an external magnetic field and retains its magnetic properties even after the field is removed. Examples include iron,nickel,and cobalt.
$A$ magnetic domain is a small region within a ferromagnetic material where the magnetic moments of all atoms are aligned in the same direction due to strong internal exchange coupling. These domains act as tiny magnets within the material.