'Rǔ huà' literally combines 'rǔ' (milk) and 'huà' (to transform or change), reflecting the original idea of turning substances into a milk-like, uniform mixture. In modern usage, it means 'to emulsify' — the process of dispersing one liquid into tiny droplets within another immiscible liquid (e.g., oil in water), typically with the help of an emulsifier like lecithin or detergent.

This term is common in food science, pharmaceuticals, cosmetics, and chemical engineering. For example, mayonnaise forms when egg yolk emulsifies oil and vinegar; intravenous lipid emulsions used in medical nutrition are also prepared through rǔ huà. While the character 乳 evokes dairy, the word applies broadly to any stable dispersion — not just milk-based ones — making it a technical verb rather than a colloquial one.