Core Inflation

What Does Core Inflation Mean?
A measure of inflation that excludes certain items which face volatile price movements. Core inflation eliminates products that can have temporary price shocks because these shocks can diverge from the overall trend of inflation and give a false measure of inflation.

Core Inflation is thought to be an indicator of underlying long-term inflation. 

Investopedia explains Core Inflation
Core inflation is most often calculated by taking the Consumer Price Index and excluding certain items from the index, usually energy and food products. Other methods of calculations include the outliers method, which removes the products that have had the largest price changes.