the.com/law of supply and demand

means The economic principle that prices rise when demand outstrips supply and fall when supply outstrips demand, with price settling wherever the two balance out.

from The concept itself emerged piecemeal in economic writing over centuries, but it was crystallized as a near-mechanical 'law' in classical economics, most famously through the work of 18th and 19th-century economists like Adam Smith and later Alfred Marshall, who formalized it with supply-and-demand curves. The phrase borrows the word 'law' from physical science on purpose — a rhetorical move to make markets sound as inevitable and impersonal as gravity, even though real markets are messier than the tidy X-shaped graph suggests.