X4

X4 or X-4 may be:

*The Honda X-4, a Japanese motorcycle
*Mega Man X4, a video game for the PlayStation and Sega Saturn
*T cell tropic HIV are termed X4
*X-4 Bantam, a research aircraft that had no horizontal tail surfaces
*Ruhrstahl X-4
*The Naish X4, a kitesurfing kite
*A common name for petroleum ether
*A four-lane PCI Express slot
*The Norteños street gang
*Ultimate X4, an X-Men and Fantastic Four cross-over in the Ultimate Marvel Universe.