The central bank policy rate (CBPR) is the rate that is used by central bank to implement or signal its monetary policy stance. It is most commonly set by the central banks policy making committees (e.g. Fed Open Market Committee). The underlying financial instrument of the CBPR varies per country and is explained in the metadata. For instance, in some countries the CBPR is the discount rate while in others it is a repurchase agreement rate.
Central bank policy rate (CBPR) data can be found in the Monetary and Financial Statistics (MFS) dataset.
Metadata for CBPR data by country can be found in IFS individual country notes.