You cannot have one parallel line. There must be another line that it is parallel to. Also, 1 symmetry is meaningless - you can have one axis of symmetry or rotational symmetry of order one. The answer will depend on which one it is.
There is no specific name - other than what you used: "a pair of parallel line segments".
Diameter
A trapezoid has two parallel sides.
If it is a square or a rectangle, then yes, it will have lines of symmetry. But if you're thinking of your typical parallelogram that does not have another name, then no, it does not have lines of symmetry. Basically, no.
rhombus
Dodecagon
A symmetrical shape. There are many different shapes that have one or more lines of symmetry and there is no other name associated with them as a group.
All convex polygons have lines of symmetry. Only concave (i.e. ones with sides that cave in) do not. If you are looking for a name of a shape that has no line of symmetry, then there aren't any with specific names.
square, septagon (heptagon)!
A Line of Symmetry.
line of symmetry
line of symmetry
i dont know dont ask me i got stuck on the same Q
Line symmetry is another name for reflection symmetry. One half is a reflection of the other half. The line of symmetry is the line where you could fold the image and have both halves match exactly.
Pentagon
soda
Which pair. Of line is parallel fghj