A four-point probe is a technique used to measure the electrical properties of materials, particularly their resistivity. It consists of four equally spaced probes that make contact with the surface of the material. The outer two probes supply a current, while the inner two measure the voltage drop, allowing for accurate calculations of resistivity without the influence of contact resistance. This method is commonly used in the fields of materials science and semiconductor research. By providing precise measurements, the four-point probe helps in characterizing materials like silicon and graphene, which are essential in the development of electronic devices.