Four-wheel drive, 4WD, or 4×4 ("four by four") is a four-wheeled vehicle with a drivetrain that allows all four wheels to receive torque from the engine simultaneously. While many people associate the term with off-road vehicles and Sport utility vehicles, powering all four wheels provides better control than normal road cars on many surfaces, and is an important part in the sport of rallying.

In abbreviations such as 4×4, the first figure is normally the total number of wheels, and the second the number of powered wheels. (The numbers actually refer to axle-ends, which may have more than one wheel.) 4×2 means a four-wheel vehicle that transmits engine power to only two axle-ends: the front two in front-wheel drive or the rear two in rear-wheel drive.

The term four-wheel drive typically describes larger passenger vehicles that may allow the driver to manually switch (sometimes with an automatic option) between two-wheel-drive mode (if available) for streets and four-wheel-drive mode for low-traction conditions such as ice, mud, snow, or loose gravel.

X4 or X-4 may refer to:

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The Crimson Avenger is the name of three separate fictional characters, superheroes who exist in the DC Comics Universe.

The original Crimson Avenger made his first published appearance in Detective Comics #20 (October 1938). He was a wealthy newsman named Lee Walter Travis who took up the identity of the Crimson Avenger to battle crime.

Travis initially dressed in a red trenchcoat, a fedora, and a red mask covering his face; except for the red coloring, he was visually similar to the Shadow. He had an Asian chauffeur/crime-fighting partner, and used a gas gun to subdue criminals, similar to the Green Hornet. Later, when superheroes became more popular than costumed vigilantes, his costume was changed to a more standard superhero outfit, consisting of red tights, yellow boots, trunks and crest, and a "sun" symbol which was recently stated to have been a stylized bullet hole.

He was trained in hand-to-hand combat in Nanda Parbat. While there he saw the future and witnessed an "unnamed" hero (Superman), and the man's selflessness and death at the hands of a monster (Doomsday). This inspired him to return to America and combat crime, first as a corruption-free newspaper owner and later as a masked crime fighter.

Michael Fred Phelps (born June 30, 1985) is an American swimmer who has, overall, won 16 Olympic medals—six gold and two bronze at Athens in 2004, and eight gold at Beijing in 2008, becoming the most successful athlete at both of these Olympic Games editions. In doing so he has twice equaled the record eight medals of any type at a single Olympics achieved by Soviet gymnast Alexander Dityatin at the 1980 Moscow Summer Games. His five gold medals in individual events tied the single Games record set by compatriot Eric Heiden in the 1980 Winter Olympics and equaled by Vitaly Scherbo at the 1992 Summer Games. Phelps holds the record for the most gold medals won in a single Olympics; his eight at the 2008 Beijing Games surpassed American swimmer Mark Spitz's seven-gold performance at Munich in 1972. Phelps' Olympic medal total is second only to the 18 Soviet gymnast Larisa Latynina won over three Olympics, including nine gold. Phelps also holds the all-time record for most gold Olympic medals, at 14.

The Honourable Usain St. Leo Bolt, OJ, C.D. ( /ˈjuːseɪn/; born 21 August 1986), is a Jamaican sprinter and a five-time World and three-time Olympic gold medalist. He is the world record and Olympic record holder in the 100 metres, the 200 metres and (along with his teammates) the 4×100 metres relay. He is the reigning Olympic champion in these three events, and is one of only seven athletes (along with Valerie Adams, Veronica Campbell-Brown, Jacques Freitag, Yelena Isinbayeva, Jana Pittman, Dani Samuels) to win world championships at the youth, junior, and senior level of an athletic event.

Bolt won a 200 m gold medal at the 2002 World Junior Championships, making him the competition's youngest-ever gold medalist at the time (since surpassed by Jacko Gill). In 2004, at the CARIFTA Games, he became the first junior sprinter to run the 200 m in less than 20 seconds with a time of 19.93 s, breaking the previous world junior record held by Roy Martin by two-tenths of a second. He turned professional in 2004, and although he competed at the 2004 Summer Olympics, he missed most of the next two seasons due to injuries. In 2007, he broke Don Quarrie's 200 m Jamaican record with a run of 19.75 s.