I guess we'll just have to disagree. They're a pretty basic data structure that's used quite often to solve a class of problems. And they're not that hard to learn. How they work is pretty simple and the reason to use them is pretty easy to grasp. I would say that there are few good software engineers out there that aren't clear on what they are at a basic level.

I am curious. Which one do you think is more difficult to understand? (I couldnt tell)