Skew is a pretty cool word, and it sounds like it means something really weird, and it kind of does. It means lines that go any which way. It describes any two lines that aren't either parallel or perpendicular to each other. Most lines are skew to each other. The two lines in this picture are skew to each other.
Remember that lines go on forever in both directions. You might have two line segments, where only part of the line was drawn on the paper. If you continued the lines out, though, they would cross each other, and not at right angles. Then those two line segments are skew to each other, even though they don't actually touch each other.