2010 TK7 is a small asteroid that precedes the Earth in its orbit; it resides at Earth's L4 Trojan point, and is currently Earth's only known Trojan asteroid. 2010 TK7 has an usual orbit, which has delayed its full description. Presumably, once its orbit is adequately described, and perhaps better spectral images gathered, it will be given a proper name.
In the meantime, the provisional name 2010 TK7 is used. This name tells us that it was discovered in 2010, and the 'T' indicates that it was discovered between October 1st and October 15th. The K7 indicates that it is the 192nd minor planet (a category that includes asteroids) discovered during that time period.
2010 TK7 is quite small, with an estimated diameter of about 300 meters. It orbits loosely around Earth's L4 point, 60 degrees ahead of us in Earth's orbit. This results in a complex path, but one that is always quite a distance way from Earth, with its closest approach being 0.197 AU (for context, the moon is 0.0025 AU away; Mars 0.52 AU), and its furthest distance being nearly 180 degrees (2 AU) from us. It also has an orbital inclination of 20.88 degrees, meaning that it is rarely actually directly in Earth's orbit -- relevant primarily because this makes it even more expensive to send a probe to visit it; unfortunately, our Trojan is not a very attractive target for space exploration.
Other planets have multiple
Trojan asteroids, and Jupiter has thousands; it is not unlikely that we will discover other Earth Trojans in the future.