Final answer:
Two lines that do not intersect and are in the same plane are known as parallel lines. These lines maintain a constant distance from each other and exemplify properties like those observed when light reflects off a flat mirror.
Step-by-step explanation:
Two lines in the same plane that do not intersect are called parallel lines. In geometry, parallel lines are lines in a plane that are at the same distance from each other and will never meet, no matter how far they are extended. This concept is critical in understanding geometric figures and in tasks such as constructing angles or working with coordinate systems. For instance, when dealing with a flat mirror and considering two rays originating from the same point and diverging at an angle, the angle between their directions remains the same after reflecting off the mirror, because a flat mirror is neither converging nor diverging. In the context of lenses, a ray parallel to the principal axis and another ray that passes through the center of the lens can be used to locate the top of an image of an object placed in front of the lens.