Speed of lightspeed of light is exactly 299,792,458 meters per second. This is the definition of a meter. A photon (particle of light) travels at this speed.
The Theory of General Relativity developed by Albert Einstein discusses the behavior of things that are travelling very fast. Objects (like rocks, planets, and spaceships) and some particles (like electrons and protons) have mass. When an object or a particle goes faster it gains mass. This means it takes more energy to accelerate it more (to make it go faster). When things are moving slowly, the increase in energy needed is small. But as their speed gets closer to the speed of light, the amount of energy needed to accelerate them becomes very, very large. The Theory of Relativity says that to make an object or particle go at the speed of light would require infinite energy, and that at this speed it would have infinite mass (more than the whole Universe). Therefore the theory of Relativity says that it is impossible to make any object or particle go at the speed of light.
This means that if we could build spaceships that could go to other stars, it would take hundreds or thousands of years to get there. Because of this, many people would like to find some way to go faster than light (sometimes abbreviated FTL). Many studies have been done on the possibility of Warp Drive, Wormholes, and higher dimensional forms of travel that could go faster. When we watch movies or television shows about spaceships, they usually use some kind of FTL like this. But in real life, these ideas are still new, and scientists don't have enough evidence yet to believe that they are really true.
Going faster than the speed of light is sometimes called breaking the light speed barrier.