Valentina,
I doubt if there would be a special name because your figure has no special properties. A foursided figure is called a quadrilateral or quadrangle, whichever name you prefer. There are special names when two of the sides are parallel  in America the figure is an isosceles trapezoid if two equal sides are not parallel while the other sides are; if no sides are parallel it is a trapezium. (In British English the meanings of the words trapezoid and trapezium are reversed!) (Your figure could not have two of the equal sides parallel because then it would be a parallelogram and opposite sides would necessarily have the same length.)
Chris
