A metallic bond forms when the valence electrons are not associated with a particular atom or ion. Instead, they exist as a "cloud" of electrons around the ion centers.
Metallic materials have a high level of electrical and thermal conductivity when compared to materials with covalent or ionic bonding. A metal such as iron has metallic bonds.
In the real and imperfect world, most materials do not have pure metallic, covalent or ionic bonds, and they may have other types of bonding. For example, iron has predominantly metallic bonding, but some covalent bonding also occurs.
Metals usually have a filled shell plus one or two extra electrons. Extra electrons in metals are not restricted to one atom but can move throughout entire structure in what is called an "electron sea." Metal atoms are positive charges in the electron sea. They are held together by the electrons. The electrons are free to move. Therefore, metals are good conductors of heat and electricity.
The metallic bond is not like an ionic bond. In a metal, all atoms are the same. There are no cations and anions, and it is not like a covalent bond. The metallic bond is not localized between two atoms, and the electrons are shared by all the atoms.