Understanding the quadrilateral In that all …

• Parallelogram: A quadrilateral with each pair of opposite sides parallel.
  (1) Opposite sides are equal.
  (2) Opposite angles are equal.
  (3) Diagonals bisect one another.
  
• Rhombus: A parallelogram with sides of equal length.
  (1) All the properties of a parallelogram.
  (2) Diagonals are perpendicular to each other.
  
• Rectangle: A parallelogram with a right angle.
  (1) All the properties of a parallelogram.
  (2) Each of the angles is a right angle.
  (3) Diagonals are equal.
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• Square: A rectangle with sides of equal length.
  (1)  All the properties of a parallelogram, rhombus and a rectangle. 
• Kite: A quadrilateral with exactly two pairs of equal consecutive sides
  (1) The diagonals are perpendicular to one another
  (2) One of the diagonals bisects the other.
  (3) In the figure  but .
  
• Trapezium: A quadrilateral having exactly one pair of parallel sides.
  
• Diagonal: A simple closed curve made up of only line segments. A line segment connecting two non-consecutive vertices of a polygon is called diagonal.
  
• Convex: The measure of each angle is less than .
• Concave: The measure of at least one angle is more than 
• Quadrilateral: Polygon having four sides.
• Element of quadrilateral:
  (i) Sides: Line segments joining the points.
  (ii) Vertices: Point of intersection of two consecutive sides.
  (iii) Opposite sides: Two sides of a quadrilateral having no common endpoint.
  (iv) Opposite Angles: Two angles of a quadrilateral not having a common arm.
  (v) Diagonals: Line segment obtained by joining the opposite vertices.
  (vi) Adjacent Angles: Two angles of a quadrilateral having a common arm.
  (vii) Adjacent Sides: Two sides of a quadrilateral having a common endpoint.

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https://mycbseguide.com/blog/ncert-solutions-for-class-8-mathematics/