Mathematical lines are, well, mathematical constructs. So they can represent things that make no “common sense” in the real world unless you realize the construct. For enample, the mathematical equation y=x represents a straight line running forever at a 45 degree angle thru the x,y axis, where x represents the horizontal axis numbers and y represents the vertical axis numbers. Yet, consider the equation y=x square - 3*x divided by x-3. Looks more complicated. Yet it also represents the same straight line, except it has a “hole” at x=3, since the denominator is zero at x=3, so the equation is undefined there. You COULD call that a non infinite line in the sense that it has a hole in it. Mathematical equations can be constructed that they can do lots of wonderful things, that are quite useful in science in engineering, but viewed in the physical plane, can make your head spin if you’re not used to the abstractions used.