Solder is a fusible metal alloy used to create strong, conductive joints between metal components, commonly utilized in plumbing, electronics, and metalwork. In plumbing, solder is typically composed of tin and lead or tin and copper and is used to join copper pipes and fittings. The solder is melted using a heat source and flows into the joint, solidifying to form a durable, leak-proof connection. Solder is essential for creating reliable and long-lasting bonds in various applications, ensuring the integrity and functionality of metal assemblies.