a square.
http://wiki.answers.com/Q/What_shape_is_the_quadri...

A regular quadrilateral is a shape with four sides which are all the same
http://www.chacha.com/question/whatisaregularq...

An angle is formed when two lines (or line segments) meet at a single point. Angles are classified into distinct groups based on their measurement in degrees. Acute angles measure
http://www.ehow.com/info_8367679_degreesquadrilat...

Rules for a quadrilateral would be to have all interior angles=360 degrees,has to have 4 sides and needs to be a closed shape.
http://wiki.answers.com/Q/What_makes_a_quadrilater...
