a polygon with 4 right angles and 4 sides of the same length
A rhombus.
A square.
"Square. Congruent means "the same". A rectangle with 4 sides that are the same is a square." Plus, it is not a rectangle. It is a polygon. The question should have been stated: What is a polygon with congruent sides?
A polygon with five congruent sides is a pentagon.
A regular polygon is a polygon with congruent sides and interior angles.
It all depends on what kind of polygon it is. It may have no congruent sides or all congruent sides.
A polygon that has congruent sides and congruent angles is called a Regular polygon. If the number of sides is given, you can be more specific. Some examples: 3 congruent sides/angles = equilateral triangle 4 congruent sides/angles = square 5 congruent sides/angles = regular pentagon 6 congruent sides/angles = regular hexagon ...and so on, by adding "regular" in front of the shape's name.
rectangle
a trapezoid
It is an equilateral polygon. It is not a regular polygon. For the polygon to be regular, it is not enough for the sides to be congruent: all the angles need to be congruent as well.
A square or a rhombus