Like Donald said, It is short for 环境卫生. Ancient Chinese believe the sky is round like a bracelet and the earth is flat. 环境 literally means "the space of the bracelet" and later extended to mean "the space around us", "situation" and "environment". 卫 = protect/guard 生 = life. The Chinese language is flexible in using old words for new situations. For example, 电 originally means lightning and is now extended to mean "electricity" and so "electric talk" 电話 becomes "telephone". Many computer terms in English also uses this method to express new terms instead of inventing new words; eg, "abort", "bug"