Metals are said to be malleable because they can be beaten into thin sheets without breaking. This is due to the nature of metallic bonding, where positively charged metal ions are surrounded by a sea of delocalized electrons that are free to move around. When a force is applied to a metal, these delocalized electrons act as a lubricant between the metal ions, allowing them to slide past each other and change shape without breaking. This property is important for the shaping of metals into various forms and structures for use in construction, manufacturing, and other applications.