Trapezoid

Whatever the fuck you want it to mean apparently!
Bob: "So it can only have one pair of parallel sides?"
Jim: "Yes!"
Bob: "So you're saying that it can have at least one pair of parallel sides?"
Jim: "Yes!"
Charles: "Wait, so, that means it can't have any parallel sides?"
Jim: "Yes!"

A square and an octagon are both trapezoids because a trapezoid has at least 2 pairs of parallel sides.

Neither a square nor an octagon are trapezoids because trapezoids can only have 1 pair of parallel sides.

Neither a square nor an octagon are trapezoids because trapezoids can not have any parallel sides. (If you're bri'ish)