This is the 3449th most frequent German word.
kern
Core; nucleus; kernel.
Here, 'Kern' refers metaphorically to the 'core' or central essence of an issue.
Der Kern des Problems liegt in der Kommunikation.
The core of the problem lies in communication.
In this sentence, 'Kern' is used literally to mean 'seed' or 'pith' as found in fruits.
Im Zentrum des Apfels befindet sich der Kern.
In the center of the apple is the seed.
In this context, 'Kern' denotes the 'nucleus' — the central structure of an atom in scientific terms.