Core CPI is the Consumer Price Index with food and energy prices removed. Both categories are volatile for reasons that often have nothing to do with the broader economy — a supply shock, a bad harvest, a geopolitical spike in oil. Stripping them out leaves a steadier signal of where prices are trending underneath the noise.
The trickiest scenario for a central bank — and one of the more common patterns in recent cycles — is when headline CPI cools (giving the impression inflation is fading) while core CPI stays stubbornly elevated. That split gives doves cover on the surface, but ties policymakers' hands underneath, since core is the number they actually use to judge whether inflation is genuinely under control.