This may be a stupid question, but this formula is just not clicking with me.

I understand the rationale behind the factorial, but I do not understand the notation after the factorial. What does it represent? Is it... the individual density functions multiplied by each other? Can someone provide a few examples of how this formula would look in action using real #s? It seems like in the examples I am looking at they always each 1?

Again I apologize for the stupid question but I need a pointer or two here!