It is multiplying probabilities. Please check out this page. The code line you quoted is the same as the first equation in the â€śMultivariate Normal Distributionsâ€ť section. And if you keep following the text, you will see that, when the features are uncorrelated, the first equation can be reduced to the 5th equation (in the same section, note number 2) which is more familiar to us.

I would check out section 4.2 - Bivariate Normal Distribution of the same link for some visuals and for a simpler, more human-brain friendly 2 dimensional case. When you feel comfortable with the 2D case, then you can go back to the N-D case, or you may try to explain to yourself about the 1-D case.