Line
Imagine that the line segment from A to B (i.e., AB) is extended beyond A in one direction and beyond B in the other direction without any end. This is a model for a line. Do you think you can draw a complete picture of a line?
A line through two points A and B is written as AB. It extends forever in both directions. Sometimes a line is denoted by a letter like l or m.
Observe that any two points determine a unique line that passes through both of them.