Thanks, that's what I wanted to know. Not blaming the user for explaining, I just didn't understand why an explanation is needed on this site of all places. Like others have pointed out, Yandex isn't only used by Russians but around the world. They clearly have the best freely accessible reverse image search since Google has impaired theirs for whatever reason. But I guess I'm in a bit of a bubble assuming that everyone knows the company.
I've asked around here to my colleagues and none of them have ever heard of it. One of them asked if it's the same as baidu :)