I'm facing confusion about the definition of the convolution between two discrete periodic signals.
Basically, the definition of convolution between s and t is defined as :
In the operation, while the index of s is increasing ([0, K-1]), we have the index of t doing the opposite [n, n-K+1].
But here for example, the convolution is also employed, but the situation is different. And from my understanding, convolution in this case could be defined as :
And now we can see that the indices of s and t are moving in the same direction and the result will be totally different if we compare it, with the first definition.
At this point, I'm hesitating between convolution, circular/cyclic convolution, or even cross-correlation. As a bonus, I'd be grateful if you could also clarify the difference between these terms.

