A quadrilateral is any polygon with four sides. So what are the Types of Quadrilaterals?

Most Common

Less Common

NOTE: Notice how a square fits the definition of a rectangle, and a rectangle fits the definition of a parallelogram, etc. One quadrilateral can be multiple things as long as it fits the definition.

Check out this Vsauce video on quadrilaterals (it's short)

NOTE 2: There is some confusion on whether a trapezoid has EXACTLY one pair of parallel sides or AT LEAST one pair.