Here's why:

* Conductors allow electricity to flow freely through them. This is because they have many free electrons that can carry the current. Examples include copper and silver.

* Insulators resist the flow of electricity. They have very few free electrons. Examples include rubber and glass.

* Semiconductors fall somewhere in between. They have a conductivity that is between that of a conductor and an insulator. This is because they have a limited number of free electrons, and their conductivity can be controlled by various factors like temperature and impurities.

Germanium's conductivity is influenced by the presence of impurities and its temperature. This makes it a valuable material for creating transistors, diodes, and other semiconductor devices.