Concept

Quadrilateral: a 4-sided figure.
Parallelogram: a 4-sided figure with opposite sides parallel.
Rectangle: a figure with 4 straight sides and 4 right angles. 
Square: a figure with 4 equal straight sides and 4 right angles.
Rhombus: a parallelogram with opposite equal acute angles, opposite equal obtuse angles, and 4 equal sides.
Trapezoid: a quadrilateral with only one pair of parallel sides.

Parallel: lines that run alongside one another without intersecting.
Congruent: having the same size and shape.

Right angles: angles that are 90°.
Acute angles: angles that are less than 90°.
Obtuse angles: angles that are more than 90°.

Rule

A square is a quadrilateral because it has 4 sides. It is also a parallelogram because opposite sides are parallel. It is a special rectangle with 4 right angles and 4 congruent sides.

A rhombus is a quadrilateral because it has 4 sides. It is also a parallelogram because opposite sides are congruent. However, it is not a rectangle because it does not have 4 right angles. Instead, it has 2 acute and 2 obtuse angles. 

A trapezoid is a quadrilateral because it has 4 sides. However, it is not a parallelogram because two of its sides are not parallel. It is also not a rectangle, because it does not always have right angles. Instead, it has 2 acute and 2 obtuse angles and one pair of parallel sides.

Example

Which quadrilateral has 1 pair of parallel sides.

Solution

Pre-requisite Skills

Identify Three Dimensional Figures (4.8.1)

Faces, Edges, and Vertices (4.8.2)

Nets of 3 Dimensional Figures (4.8.3)

Simple Polygons (4.9.1)