The short-run relationship between inflation and unemployment is often called the Phillips curve.
Economist A. W. Phillips published a study in 1958 showing an inverse historical relationship between unemployment and wage inflation in the United Kingdom. Later versions connected unemployment with price inflation more broadly. The basic short-run idea is that stronger demand can raise employment while also putting upward pressure on wages and prices.
The relationship is not a permanent menu of choices. Milton Friedman and Edmund Phelps argued that expectations matter: once workers and firms adjust their inflation expectations, unemployment tends to return toward a longer-run level. This led to the distinction between a short-run Phillips curve and a long-run version that is often drawn as vertical.
The curve is therefore a model, not a mechanical law. Supply shocks, changing expectations, labor-market institutions, and productivity can all affect the observed relationship.