A pin header (or simply header) is a form of electrical connector. A male pin header consists of one or more rows of metal pins molded into a plastic base, often 2.54 mm (0.1 in) apart, though available in many spacings. Male pin headers are cost-effective due to their simplicity.
Pin header connectors comprise several different means of connection. The most commonly seen pin headers are 0.1″ (2.54mm) single or double row connectors. This is a standard breadboard compatible pitch. These come in male and female versions, and are the connectors used to connect Arduino boards and shields together.