Metal in girders refers to STEEL, which is a type of metal alloy composed of iron and carbon. STEEL is one of the most commonly used materials in construction due to its strength and durability. It is often used in girders, which are structural beams that support the weight of a building or bridge. STEEL is also used in other construction projects such as bridges, buildings, and even ships. STEEL is an essential component of modern infrastructure and is used in many industries.