what is meant by point if inflection

a point where curve changes its concavity like in graph of x cube its on origin

A point of inflection is a point where a f(x) changes its sign i.e from positive to negative or from negative to positive. That is nothing but local maxima or minima for f(x). 

its a point in the domain of the function where the corresponding curve changes from convex to concave or concave  to convex