Geometric half-line primitive; drawn in Graphics3D clipped to the plot range
HalfLine[{p1, p2}]
HalfLine[p, v]
ArcLength[HalfLine[{0, 0}, {1, 1}]]
→ InfinityGraphics3D[HalfLine[{0, 0, 0}, {1, 2, 3}]]
→ -Graphics3D-Graphics[HalfLine[{{0, 0}, {1, 0}}], Frame -> True]
→ -Graphics-