A line, just like a point, is an undefined term. It is a one-dimensional object of infinite length with no width or height that never bends or turns. Its graphical representation is a straight line with arrowheads on either end, indicating that it continues indefinitely in both directions.
For each pair of non-identical points, it is possible to draw exactly one unique line through them. Thus, a line can be named using any two of the infinitely many points that lie on it. The above line could be named or line A set of two or more points that lie on the same line is said to be collinear.