There are many different types of quadrilaterals: squares, rectangles, rhombuses, trapezoids, parallelograms and kites. A quadrilateral defined as a closed shape (polygon) that consists of exactly four straight lines.
There are only three properties that every quadrilateral shares. They must all have four sides, four vertices and four internal angles with a total sum of 360 degrees.
The simplest type of quadrilateral is the square. A square can be any size, but all of its sides must be the same length, and both sets of opposite sides must be parallel to each other. The internal angles must also be exactly 90 degrees.
A rectangle is similar to a square in that opposite sides are parallel and equal in length to each other, but not all sides must be the same shape. A square fulfills all these conditions and is a special type of rectangle.
The rhombus shares almost all the properties of a square, with four equal sides and parallel opposite sides. However, while opposite angles need to be equal, angles do not need to be 90 degrees.
Trapezoids and kites are two quadrilaterals where the opposite sides do not need to be parallel. They are the most general quadrilaterals, and every other quadrilateral fits the definition for either a trapezoid or kite.