Why is the greek letter Pi used for Pi (product) notation?

Question

We are learning about it and my teacher didn't explain why either Sigma nor Pi were used.

Answer 1

It's phonetic - $\Sigma$ stands for "sum" and $\Pi$ stands for "product.

Answer 2

$\pi$ is a capital letter from the Greek alphabet called “Pi", it corresponds to “P” in our alphabet. So, "p"roduct notation is derived from the symbol of "Pi", $\pi$. A similar reasoning holds for the summation symbol, sigma.