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But in general sense lint-free simply means that the cloth does not leave streaks and fibers behind when you wipe a surface with it. From that it kind of branches out into different grades of "lint-freeness" from scientific at $70+ per box where you absolutely cannot have any fiber whatsoever (say, you're using a microscope to look at a thing that's smaller than the fiber itself - happens a lot in fiber optics) all the way down to $3/bundle of lint-free towels for drying your car with. The $3/bundle towels do leave some lint behind but not much and whatever is there will be blown off as soon as you start driving.
For wiping computer and PC screens you want to be somewhere in the middle. You would not want visible fibers left but 1 or 2 on the entire screen is not going to be all that critical. Check out this Amazon page: