Humus (fǔzhízhì) is the dark, organic material formed in soil when plant and animal matter decomposes fully over time. It’s rich in nutrients and essential for healthy soil structure, water retention, and plant growth. The three characters reflect this process: 腐 means 'rotten' or 'decayed', 殖 means 'to multiply' or 'to reproduce'—here suggesting biological activity and microbial proliferation—and 质 means 'substance' or 'material'. Together, they describe the stable, nutrient-rich substance resulting from natural decomposition.

This term is used primarily in agriculture, ecology, and environmental science—not in everyday casual speech. You’ll encounter it in discussions about soil fertility, organic farming, composting, and ecosystem health. While not commonly used in daily conversation, it appears frequently in textbooks, scientific articles, and sustainability education in Chinese-speaking regions.