They are both plane figures bounded by straight sides.
It is not a quadrilateral because quadrilaterals are figures that have four sides (thus the use of quad meaning four). A triangle only has three
yes they are all four sided figures classifying them as quadrilaterals
A quadrilateral with two parallel sides is a trapezoid.
A Quadrilateral. Figures that have four equal sides are called squares. Whereas, other figures that have four unequal sides are called quadileterals
There are infinitely many plane figures, not just five! A circle, ellipse, A triangle, quadrilateral, pentagon, hexagon, heptagon, octagon, and on and on. And then there are mixed figures such as a semicircle, a segment of an ellipse. Not forgetting plane figures that have "random" boundaries.
There exists at least one quadrilateral which is not 4-sided.
Yes, you may think of "closed figure" as part of the definition of a quadrilateral.
It means four sides, and refers to plane figures bounded by four straight sides.