Sentence:  Another commonly used Japanese term in matsutake literature is "<WSD>shiro</WSD>". As a Japanese noun,  it means castle or domain (fruiting place) of a  mushroom. As an adjective, it means white. More specifically, a <WSD>shiro</WSD> is the dense mat of fungal filaments ("hyphae" or collectively "mycelium") that matsutake species form in the soil. 
Meaning of the word marked with <WSD> tags:  A mass of hyphae constituting the mycelium of certain fungi.