The speed that light travels (if it doesn't say in what medium, then it implies the speed that light travels *in vacuum*) Light travels at 2.99792458E8m/s, or approximated to 3.0E8m/s, in vacuum. Due to the lazy nature of physicists, this number is commonly denoted as a constant c in calculations. The Theory of Relativity predicted that no moving object in the universe has a speed that exceeds c. Therefore, if you hear something is traveling faster than the speed of light, it's non sense.
A light-year is the distance that light can travel in a year. The speed of light is about 3.0E8m/s, and a year has 3.1536E7 seconds. Therefore, a light-year is about 9.46E15 meters.