This term describes all living beings that can decompose wood. These are only very few, since wood has a fibrous and stable structure of cellulose and lignin. Some fungi grow directly on the wood and grow through it with their hyphae. The hyphae excrete enzymes that decompose the wood and then the nutrients are absorbed. This process is also called "exogenous digestion", i.e. digestion that takes place outside the organism.
Explanation for children:
Wood decomposers are living beings that can break down wood, such as some fungi. The fungus grows on top of the wood, and its fungal filaments do the decomposition. They grow through the wood and excrete substances that not even the strong wood can withstand. The fungus can then absorb the available nutrients from the wood. This type of digestion is called exogenous digestion because it takes place outside the fungus. For us, digestion is endogenous because our decomposing substances are in the mouth and stomach.