Rosin-core solder is a type of solder used primarily in electronics for joining metal components. It consists of a metal alloy, usually made of tin and lead, with a core of rosin flux. The rosin helps clean the metal surfaces during soldering, ensuring a strong electrical connection. When heated, the rosin melts and flows, allowing the solder to bond effectively to the surfaces being joined. This type of solder is favored for its ease of use and effectiveness in creating reliable connections in circuit boards and other electronic devices.