Question

what is mycelium?
a chemical compound found in mushrooms
a synthetic material used in shoe production
the interlocking root system that spawns mushrooms and fungi
a type of leather used in fashion

Explanation:

Mycelium is the vegetative part of a fungus, consisting of a network of fine white filaments (hyphae). It is responsible for nutrient absorption and forms the basis for the growth of mushrooms and other fungi. It is not a chemical compound, synthetic material, or type of leather.

Answer:

The interlocking root system that spawns mushrooms and fungi.