Definition: A kite is a quadrilateral with two distinct pairs of adjacent congruent sides; one diagonal is the perpendicular bisector of the other.
What defines a kite?
Two sides next to each other are equal, and the other two sides next to each other are equal too, with the pairs different from each other. The shape looks like a flying kite.
Which properties hold?
The diagonals are perpendicular. The diagonal that joins the vertices between the equal sides bisects the other diagonal and also bisects the angles at its ends. One pair of opposite angles, those between unequal sides, are equal.
Example. A kite has diagonals 18 and 10. Area = (1/2)(18)(10) = 90. Suppose the long diagonal is cut into parts of 12 and 6, while the short diagonal is cut into two halves of 5. The two longer sides are the square root of 144 + 25, which is 13. The two shorter sides are the square root of 36 + 25, which is about 7.81.
What mistakes occur?
Treating a kite as a parallelogram; its opposite sides are not parallel. Another error is applying the area formula with the sides rather than the diagonals. Remember that a rhombus counts as a kite in some definitions.