a solid line at the edge of a paragraph.
It can be a border.
The margin.
border
A margain could be drawn on any edge of a paraghraph.
Border
A separator or a horizontal line.
The answer is border.
The line that forms the edge of a figure is an edge line. Which forms the figure the has been drawn. You use this line to define a drawing or a figure.
contour line
contour line
The edge is a line - straight or curved - where two faces of the solid meet.
Its perimeter
outline
outline
An edge is a line at which two faces of the solid meet.