Among the given options, number 3 is accurate. A line is classified as an undefined term since it represents something that lacks width or depth, yet it can extend infinitely in both directions, indicated by arrowheads.
The terms point, line, and plane are considered undefined. When attempting to define these terms, it's necessary to depend on other terms that also require definitions. Mathematicians use a broad description to convey the concepts of these terms rather than providing a strict definition. The answer is indeed a term with no formal definition.
