Point at Infinity

$P$ is the point on the line $AB$ such that $\overline{PA}/\overline{PB}=1$. It can also be thought of as the point of intersection of two Parallel lines.

See also Line at Infinity

References

Behnke, H.; Bachmann, F.; Fladt, K.; and Suss, W. (Eds.). Ch. 7 in Fundamentals of Mathematics, Vol. 3: Points at Infinity. Cambridge, MA: MIT Press, 1974.