The Meissner effect is an important property of superconducting materials.
When a material becomes superconducting below its critical temperature, it expels magnetic field from its interior.
This expulsion of magnetic flux is called the Meissner effect.
It shows that a superconductor is not just a perfect conductor, but also a perfect diamagnetic material.
Insulators do not conduct electricity.
Conductors allow electric current but do not show complete magnetic flux expulsion.
Semiconductors have conductivity between conductors and insulators.
Only superconductors exhibit the Meissner effect.
Therefore, the correct answer is:
\[
\text{Superconductor}.
\]