On the left, the four lines are the historical policy rates from G4 central banks (U.S., euro area, UK and Japan). In the case of the UK, Japan and euro area, policy rates have remained low for much of the post-global financial crisis era. The U.S. did begin its interest rate hiking cycle in 2017 but this was interrupted by the U.S.-China trade tension and then the COVID-19 pandemic.
On the right, the four lines show market expectation of where policy rates would be in coming years. For now, investors are expecting central banks to maintain low policy rates for an extended period of time despite the recent rise in inflation.