When we draw lines on a piece of paper without  lifting the pencil and without using a scale, the shapes that we get are called curves. 
Simple Curve : A curve that does not cross itself is called a simple curve. The figures  shown below are simple curves.

Open Curves : The figures that do not begin and end at the same point are called open curves.

Closed Curves : The figures that begin and end at the same point are called closed curves. 
For example : triangle, circle, rectangle, square, etc. are all closed figures.

Position in a figure                                               
    In a closed curve, thus, there are three parts.
    (i)     interior (‘inside’) of the curve
    (ii)     boundary (‘on’) of the curve and
    (iii)     exterior (‘outside’) of the curve.
    In the figure, A is in the interior, C is in the exterior and B is on the curve.
    The interior of a curve together with its boundary is called its “region”.

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