A quadrilateral. It may be a rectangle, parallelogram, trapezoid, or an irregular quadrilateral.
always
sometimes
A rhombus.
trapezoid
A general quadrilateral has no equal sides, but it also has no specific name. Among quadrilaterals with a name, a trapezium (unless it is isosceles) can have no equal sides.
No, a quadrilateral must have 4 sides. If it is a proper quadrilateral it must have 4 sides of equal length but if it is an irregular quadrilateral it must have 4 sides but not have equal sides. An example of a quadrilateral could be a square. A pentagon on the other side must have 5 sides.
It is a rectangle
There is no specific name for such a quadrilateral.
square
All quadrilaterals have two [pairs] of opposite sides and in most cases they are not equal.
Many different types of quadrilaterals can have three equal side lengths. as long as it is a closed shape that has four sides, it is considered a quadrilateral, but not all quadrilaterals have names. A triangle with three equal side length would be called an equilateral triangle.