CORE stands for Categories Of Rhythmic Elements
This is the Theory Part.
The CORE part has the image of the core of an apple because this is where the apple was built from. CORE is the part where rhythmic theory is bundled.
Think of it this way. If you want to enjoy an apple you don’t have to worry about the core. You eat the apple and toss the core when you’re done. But if you want to grow a tree or an entire orchard, you better understand exactly how the core and its elements can be cultivated into much more.