“Core” inflation is a term the government made up to cook the books and give us phony numbers and make us feel all warm and fuzzy about the state of the U.S. economy. Real inflation rates are thus concealed.
Core inflation is measured by taking out the index items that are susceptible to abrupt price movements. This will include food and energy (yeah, like those aren’t important!) and other items from time to time. The high oil prices, for example, even though they affect every other price to which gas is a factor (most things), are not reflected in core numbers.
Anytime you hear the word “core” in the mainstream media when a discussion about inflation arises, turn on your B.S. detector and move on!