Malleability is a mechanical property of matter, but is most commonly used in reference to metals and metalloids. A malleable metal is capable of being flattened into thin sheets without cracking by the processes of hammering or rolling. This property is important in metalworking, as materials that crack or break under pressure cannot be hammered or rolled. Malleable materials can be formed using stamping or pressing, whereas brittle metals and plastics must be molded.
Malleability occurs as a result of the specific type of bond found in metals (Main article: metallic bond). In metallic bonds, valence shell electrons are delocalized and shared between many atoms. This is often referred to as the "sea of electrons" and is responsible for many properties of metal. The delocalized electrons allow metal atoms to slide past one another without being subjected to strong repulsive forces that would cause other materials to shatter.
It also means changeable, as in "we are all malleable".