Metallic bonds are a type of atomic or chemical bond that occurs between metallic elements only and as its name indicates it is the process in which two atoms of the same metal or of a pure metallic compound, but not in alloys. Remember that alloys are a homogeneous mixture that solidifies but does not contain any chemical reaction.
Metallic bonds are what make a metal have the solid state of aggregation, since it joins the atoms with each other. Under certain conditions, metals present a typical geometric configuration of the compact packing of spheres (geometric figures possible through the perfect packing of spheres which allows them to create almost perfect geometric shapes such as cubes, triangles, hexagons, complex polyhedra and in the case of mercury and gallium that can create perfect spheres due to their state of liquid aggregation.
Metallic bonds are what makes metals so strong, since the greater the number of atomic bonds (protons and electrons), the greater the hardness of the metal. It is also for this reason that metals conduct electricity with little resistance and have a very high melting point.
Metallic bonds are in turn covalent bonds, so it is common for atoms to share some pairs of electrons with the atoms around them, which is the reason for the characteristics mentioned above. Any amount of a metallic element in its pure form is an example of an ionic bond.
Examples of metallic links: