Further information.

What is a kernel

As described in the Jupyter notebook beginner guide https://jupyter-notebook-beginner-guide.readthedocs.io/en/latest/what_is_jupyter.html#kernel:

A notebook kernel is a “computational engine” that [runs] the code contained in a Notebook document. The ipython kernel, referenced in this guide, [runs] python code. Kernels for many other languages exist (official kernels).

As shown in Figure The relationship between the kernel and the notebook. the notebook is where the instructions are written but until they are sent to the Kernel the instructions will not have any effect.

Fig. 34 The relationship between the kernel and the notebook.

What other kernels can be used

You can see a list of all the various programming languages for which a Jupyter kernel exists here: https://github.com/jupyter/jupyter/wiki/Jupyter-kernels.