There is no specific name for such a shape.
An irregular polygon.
pentagon
It is an undecagon
A plane shape with these characteristics is a "hexagon".
Not possible ! If the shape has four right-angles, at least two sides must be the same length.
An irregular hexagon
Either scalene triangle or a circle
A better name for "corners" would be angles, but the shape's name would be a hexagon
A parallelogram
That's an irregular quadrilateral.
A shape with more than four sides, but has four right angles. There is no name for it.