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.

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Also the name of a group of fortresses in Italy.