A set of relationships based on past friendship or acquaintance that sometimes replaces or undermines official organizations: “He didn't deserve that promotion; he got it because of his connections to the old boy network.”
A reciprocally supportive, exclusive, and influential group of men, esp those who were friends at some prestigious school or college; in-group: an ''old-girl'' network to rival the much-ballyhooed ''old-boy'' network/ It's an old boys' system. Once you have a few commissions under your belt, one architect recommends you to another (1959+ British)