A square is a four-sided polygon with two congruent parallel sides.
A four-sided polygon with opposite sides parallel and all sides congruent is a square.
Rhombus (or square).
A parallelogram.
A square or a rhombus
There is no particular name. It need not be a regular polygon - for example, consider a stretched hexagon.
A four-sided polygon with opposite sides parallel and all sides congruent is a square.
Any polygon with an even number of sides can have opposite sides that are congruent and parallel.
a trapezoid
A four-sided polygon with all sides parallel and congruent is a rhombus. If all the angles are equal, it is a special case of a rhombus called a square.
A rectangle is a quadrilateral with opposite sides parallel and congruent and four right angles. If all four sides are congruent, it is a square.
A rectangle is a quadrilateral with opposite sides parallel and congruent and four right angles. If all four sides are congruent, it is a square.
A general quadrilateral is a four sided polygon with no parallel sides and no congruent sides.
Rhombus (or square).
A parallelogram.
Any polygon with 2n sides (n integer) where opposite sides are parallel, will have its opposite angles congruent.
A four-sided polygon with congruent sides and angles, and two pairs of parallel sides.
A square or a rhombus