A quadrilateral is a word used in mathematics to describe a shape having four sides and four vertices. The word ‘quadrilateral’ is derived from the Latin word ‘quadri’ meaning variant of four and ‘latus’ meaning side.

All quadrilaterals also have four angles, a sum of 360 degrees is obtained when all the inner angles of the vertices are added. Some quadrilaterals are convex and some are concave depending on the outer form of the shape.

Shape having no side or vertices like the circle is not a quadrilateral, but figures occurring inside a circle as quadrilateral is called cyclic quadrilateral or chordal quadrilateral.

There are six basic shapes that fall in the taxonomy of quadrilaterals:

### Square:

1. All sides are equal
2. Opposite sides are parallel
3. Diagonal lines intersect making 90°
4. All angles at vertices are 90°

### Rectangle

1. Opposite sides are equal
2. Opposite sides are parallel
3. All angles at vertices are 90°
4. Diagonal lines intersect at the centre

### Rhombus

1. All sides are equal
2. Opposite sides are parallel
3. The diagonal line intersects making 90°

### Parallelogram

1. Opposite sides are equal
2. Opposite sides are parallel
3. Diagonal lines Intersect at the centre

### Trapezium

1. One pair of the opposite line is parallel
2. It forms a shape of an irregular rectangle
3. It has a larger base and a smaller top line
4. The angles at the bottom vertices are equal
5. The angles at the top vertices are equal

A convex quadrilateral is a four-sided figure or shape in which all inside angles at the vertices add up to 180 degrees or less. Convex quadrilaterals are mostly in irregular shape and have angles of lesser degrees.

A concave quadrilateral is a four-sided shape or figure in which all inside angles at the four vertices add up to more than 180 degrees. Concave quadrilaterals mostly have shapes with parallel sides and larger angles.