The word “core” has four meanings: 1). the center part of certain types of fruit, 2). the center or the most important part of something, 3). the central part of a planet, that which is in the middle, 4). relating to inflation, sudden and temporary price changes.
For our purposes here we are interested in the first two meanings. The first one refers to fruit as in the following examples. “Usually we don’t eat the core of apples.” “The core is tough and contains the seeds.” “You will need to core the pear before eating it.”
The second one refers to that which is most important, as in the following examples. “Students must take core classes before they can graduate.” “We need to get to the core of the problem before we can solve it.”
core classes, core values, down to the core, at its core