There are many different operators, for example sums

$$\sum_{i=1}^\infty$$

or products

$$\prod_{i=1}^\infty$$

But what does this operator stand for? What does it mean?

$$\mathop{\LARGE\mathrm K}_{i=1}^\infty$$

I am sorry for this might being a dumb question, but I tried googling things like "big K operator math" and didn't found anything.