On the left, the four lines are the historical policy rates from G4 central banks (the 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. is raising rates again having recovered from the pandemic and facing considerable inflation pressure.
On the right, the four lines show market expectation of where policy rates would be in coming years. Investors are reflecting a more hawkish sentiment with the U.S. Federal Reserve and the Bank of England, with policy rate hikes in 2022. The Bank of Japan is still a ways off from any meaningful tightening.