Everybody needs to understand skew lines :) .....before they take any end of course test.
Skew lines are lines that do not lie in the same plane. That is, they are noncoplanar. Think of two lines that are not parallel, yet they do not intersect. Those lines are skew lines.
The lines in this drawing are skew lines. They are not in the same plane. The do not intersect. They are not parallel.