A pattern of social coordination that emerges from the actions of many individuals none of whom intends or designs the overall result, as with language, markets or common law.
In more detail
Friedrich Hayek, borrowing from Adam Ferguson, called such orders the result of human action but not of human design, and contrasted grown orders (cosmos) with made orders (taxis). The idea supports arguments for decentralised rule-making, but it does not show that every emergent order is efficient or just.