Although concealment and misdirection of adversaries are primordial acts, the word “camouflage” did not enter the English language until World War I. Author Nicholas Rankin observed in his book “A Genius for Deception” that “the Oxford English Dictionary’s first example of published usage is from the Daily Mail in May 1917: ‘The act of hiding anything from your enemy is termed “camouflage”.'”
Nearly a century later, there is a full-fledged theory of camouflage, which is neatly presented in a new U.S. Army manual (pdf). The theory carefully distinguishes among related techniques such as hiding, blending, disguising, disrupting and decoying, each of which means something different.
The manual provides practical advice. When selecting foliage for camouflage, “coniferous vegetation is preferred to deciduous vegetation since it maintains a valid chlorophyll response” — against an enemy’s infrared sensors — “longer after being cut.”
And it reflects the lessons of experience. “Warfare often results in personnel losses from fratricide. Fratricide compels commanders to consider [camouflage's] effect on unit recognition by friendly troops.”
See “Camouflage, Concealment, and Decoys,” Army Tactics, Techniques, and Procedures 3-34.39, November 2010.