Can someone help elaborate the below statement?

Question

Python has several different implementations, written in various languages.
The version used in this course, CPython, is the most popular by far.

Answer 1

Originally Python was written in C language, that's why the most popular variant is called CPython.
This sort of defines the language capabilities (specification).
Some people decided to rewrite Python in other languages or for specific platforms (Java, C#) , these are the alternate implementations such as Jython, IronPython, PyPy. Each may have a specific merit or use case scenario. Note that the alternate implementations may not be brought up to the same version as Cpython (currently 3.8), so their syntax corresponds to some older versions.
Read more here:
https://docs.python.org/3/reference/introduction.html#alternate-implementations

Answer 2

This helps and clarifies my concern. Thank you