a right angled triangle
A 4 sided shape
a square
irregular square or rectangle
A shape with no right angles and one pair of parallel lines would be called a trapezoid in the USA, and a trapezium in Britain.
A pair of infinitely long parallel lines.
A trapezoid
A right angle triangle
A right-angle triangle.
a right angled triangle
A Trapezium is a four sided shape with only one pair of parallel lines.
A 4 sided shape
At least one pair, or one pair? If it is one pair, then it depends if the shape is regular or irregular.
A trapezoid is a four-sided figure (or "quadrilateral") with only one pair of parallel sides.
a square
Trapezoid
irregular square or rectangle