Magnetic domains are small regions within a magnetic material where the magnetic moments of atoms are aligned in the same direction. In these areas, the magnetic fields reinforce each other, creating a stronger overall magnetic field. When a magnetic material is unmagnetized, these domains point in random directions, canceling each other out. When an external magnetic field is applied, the domains can change their orientation. Some domains may grow larger while others shrink, aligning more with the external field. This process is what allows materials like iron to become magnetized and is fundamental to the operation of devices such as magnets and transformers.