Quadrilateral

In geometry, a quadrilateral is a polygon with four sides and four vertices. Quadrilaterals are further classified as follows:

Trapezium: two of the opposite sides are parallel.
Isosceles trapezium: two of the opposite sides are parallel, the two angles incident with each side are equal.
Parallelogram: opposite sides have equal length, opposite sides are parallel, opposite angles are equal.
Kite: two adjacent sides have equal length, the other two sides have equal length, opposite angles are equal.
Rhombus: four sides have equal length, opposite sides are parallel, opposite angles are equal.
Rectangle: opposite sides have equal length, opposite sides are parallel, each angle is a right angle.
Square (regular quadrilateral): four sides have equal length, opposite sides are parallel, each angle is a right angle.

Better illustrations needed.

Also the name of a group of fortresses in Italy.