The regions in a metal showing magnetic characteristics are called:

The regions in a metal that exhibit magnetic characteristics are known as domains. When discussing ferromagnetic materials, for instance, such as iron, these domains are small areas within the material where the magnetic moments of atoms are aligned in the same direction. The overall magnetic behavior of the material depends on the orientation and alignment of these domains.

In the absence of an external magnetic field, these domains can point in random directions, which results in no net magnetic effect. However, when subjected to an external magnetic field, many of these domains can align in the direction of the field, enhancing the material's overall magnetism. This understanding is pivotal in applications involving magnetic materials, including data storage and electric motors.

The other terms listed do not accurately describe these regions: lattice structures refer to the organized arrangement of atoms in a crystal, cells could refer to various configurations but are not specific to magnetic properties, and planetary spins typically pertain to celestial movements rather than magnetic behavior in materials. Thus, the term "domains" is clearly the most appropriate in this context.