In groups of hens there is a hierarchical social system in which each bird is ranked in order of dominance. The top bird is permitted to peck all lower birds, while the second highest bird is allowed to peck all the birds below her, and so on. Almost immediately after this phenomenon was documented in the 1920s (first by Norwegian zoologist Thorleif Schjelderup-Ebbe), the phrase pecking order entered the English lexicon as a metaphor for any such hierarchical system.
In business, for instance, the owner of a company is at the top of the pecking order, followed perhaps by the manager, then the assistant manager, then the worker most favored by management, and so on until we get to the temps or interns at the bottom who are pecked by everyone. Similar hierarchies are also common in government and in military units (and some argue that pecking orders exist in all human groups).
The phrase is occasionally misspelled (most often in English-language Indian publications, it seems) in various ways, including packing order, peking order, and peaking order, none of which makes logical sense.
Observing the habitual and almost sacred ‘pecking order’ which prevails among the hens in his poultry yard—hen A pecking hen B, but not being pecked by it, hen B pecking hen C and so forth—the politician will meditate on the Catholic hierarchy and Fascism. [Point Counter Point, Aldous Huxley (1929)]
The one who can use the dirtiest word is the one who wins out in the pecking order. [Etc: Review of General Semantics (1943)]
Understanding neither themselves nor their own purposes, … the core of the residential school operating personnel can fall back upon only the pecking order—mechanisms of very primitive social organizations. [Culture and Human Values, Jacob Abram Loewen (1961)]
In this coming period, rural areas will not ‘develop’ any more than they have in the past, although of course some selected areas may improve their relative standing in the world pecking order of surplus extraction. [The Capitalist World-Economy, Immanuel Wallerstein (1979)]
The cheetah’s desperate and, this time successful ploy to save her cubs also certainly reflected her place at the bottom of the major-predator pecking order, which can cause a cheetah to be attacked and driven off kills not only by lions but also by leopards, hyenas, and wild dogs. [Big Cats: Kingdom of Might (1996)]
The road back the following season was very tough, having slipped back in general fitness and the rugby pecking order. [Irish Times (2013)]