A polygon, but only if it has no curves.
If they are straight sides, then a polygon. Otherwise, simply "a closed plane figure with 3 or more sides".
A pentagon. A closed figure means that all the lines of the figure are connected.
This closed figure, with straight sides, is known as a Polygon.
It is a heptagon.
square
no.
A polygon.
A hexagon.
Add together the length of its sides. The accumulated lengths of its sides is the perimeter.
If none of the sides ever cross each other, there cannot be a closed plane figure.
Any closed figure that is not entirely composed of straight sides, such as an ellipse or a circle.