That's just a weighted average.

Suppose you want to average two numbers, X and Y. Normally you'd do this: (X + Y)/2.

But what if you want to give more weight to X than to Y? Well, then you can assign them different numbers, say r and s, and then the weighted average is (rX + sY) / (r + s).

Those numbers can be any positive number? All that's important is their relative sizes. The bigger number will have more weight in the average.

If the weights are equal, r = s, then it reduces to the normal average.

So the IMDB rating is a weighted average of R and C, and they've used those things v and m as weights. I don't know what v and m mean exactly so why they thought that made sense to use as weights. You can weight in any way that makes sense to you.