mycelium

Japanese: mycelium

…The branched, thin filamentous bodies that make up the main body (vegetative body) of fungal plants are called hyphae, and a collection of these is called a mycelium. Hyphae grow by apical growth, and as long as there is organic matter to provide nutrients, and the appropriate external conditions such as humidity and temperature continue, they will continue to grow indefinitely.

From [Fungi]

…In these respects, they are fundamentally different from prokaryotes such as bacteria and viruses. The vegetative body consists of thread-like cells called hyphae, and a loose collection of these hyphae is called a mycelium. Some are single-celled, and in yeasts they repeatedly grow by budding. …

*Some of the terminology explanations that mention "mycelium" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…真菌植物の本体(栄養体)を構成する分枝した細い糸状体を菌糸といい，その集まりを菌糸体myceliumという。菌糸は先端生長によって伸長し，栄養分となる有機物があり，適当な湿度や温度などの良好な外的条件が続くかぎりいつまでも生長する。…