I have heard a lot of people saying "Jupyter" with "py" as in Python, while others say "Jupyter", with "py" as in the name of the planet. So, what is the most correct form?
Fortunately, there are many videos and podcasts with Fernando Pérez and Brian Granger, core developers of IPython/Project Jupyter and we can easily check them. They say Jupyter with "py" as in the name of the planet. Here is an example of Fernando Perez talking about Jupyter, in PLOTCON 2016: Fernando Perez, The architecture of Jupyter.