The bolded line represents a line segment rather than a line or a plane.
What is a line?
A line refers to an infinite figure that extends to the sides. For example, the railway track is composed of two lines.
What is a line segment?
This differs from a line because it is not infinite, instead, it is a section of a line with two endpoints. This concept applies to the bolded section of the tile because the section shows only a section of a line between two corners rather than a complete line.
Learn more about lines in: https://brainly.com/question/2696693
