what kind of people is a dork?

"You know that we have always walked a fine line in order to protect our people without becoming a danger ourselves."

walk a fine line?
What kind of PERSON (singular) is a dork - Dork isn't used as much these days. It's a slang word and is negative. A dork is similar to a jerk. Or nerd or a geek (though geek isn't quite so negative, I hope). Someone who asks dumb questions, isn't very cooperative, isn't popular, is perhaps more smart than good looking. "Don't be such a dork!" is a common way to use it, meaning you should be easier to get along with in whatever matter is being discussed.

For the fine line, imagine a path with something bad on the right side, and something also bad (but perhaps the opposite of the other thing) on left, and you are walking a path or a line between them. For example, on the one side is being such an overprotective parent that your children never learn to do anything by themselves, and on the other is paying so little attention that your children are in danger. While you're "on the middle road" (another expression), you aren't doing either of those bad things. But sometimes, it's harder and harder to know where you need to be - the path gets narrower and narrower - it's easy to find yourself walking too far to the right or the left. As the path gets narrower, the line gets finer. So when you have to walk a fine line, it's hard to do it exactly right and keep both of those bad things in balance.
walk a fine line: play a balancing act between opposing tendencies, etc, like a circus artist on a wire
Students: Are you brave enough to let our tutors analyse your pronunciation?
thank you very much. god, english is so complicated

Kanonathenathank you very much. god, english is so complicated

you might want to buy Spears, Dictionary of American Idioms, a very good book, and learn 10 idioms (or more ) a day

thank you.

is this only used in America? I'm living in Australia right now
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Kanonathenais this only used in America? I'm living in Australia right now

I'd say there are many general idioms too, but it's focussed on US usage indeed.
You might want to look also at the Cambridge Idiom Dictionary for your part of the world, not sure.