Final answer:
A superconductor is a material with zero electrical resistance and perfect diamagnetism, useful in applications like MRI machines and power transmission. They must be cooled to low temperatures to work, but high-temperature superconductors are being developed.
Step-by-step explanation:
A superconductor is indeed a material that has zero resistance to electrical current. However, the perfect definition of a superconductor should also include its property of perfect diamagnetism, which becomes apparent through the Meissner effect. This means that superconductors repel magnetic field lines, maintaining a net magnetic field of zero within the material. Superconductors are incredibly useful in applications like MRI machines and power transmission, where they enable high currents without heat loss. Despite these remarkable properties, superconductors have to be cooled to very low temperatures, often just a few kelvin above absolute zero, to exhibit superconductivity, which can be costly. Recent advances in high-temperature superconductors are promising, with the potential of developing superconductors that function at or near room temperature, greatly expanding their practical applications.