the.com/pecking order

means The informal ranking of who outranks whom in a group, determining who gets deferred to and who does the deferring.

from Coined in the 1920s by a Norwegian zoologist studying barnyard chickens, who noticed hens peck subordinate birds without retaliation, establishing a strict dominance hierarchy enforced by beak. The term stayed in poultry science for a couple decades before people realized it described the office, the schoolyard, and the family dinner table just as well — and 'pecking order' flew the coop into everyday English by the mid-20th century.