If you're interested in space or space travel, you've heard of SpaceX. This is the rocket company headed by billionaire inventor Elon Musk, who is also responsible for Tesla electric cars.
SpaceX has already successfully sent supplies up to the International Space Station, and could soon be transporting astronauts up there, which is already more than most governments can manage. However, to bring the cost of space travel down, it's given itself an ambitious goal of making a self-landing reusable rocket.
Historically, rockets go up and either stay in space, burn up in the atmosphere or come crashing into the ocean. In other words, you spend untold millions on a rocket and only use it for a single flight.
If you could bring the rocket back down safely, though, you could reuse it and save a lot of money. That was also the idea behind the space shuttle, although getting each of those reconditioned for the next flight was still a major, and expensive, undertaking.
SpaceX's eventual goal is a rocket that can be reused several times in a row before needing a serious overhaul. We say "eventual" because so far it hasn't successfully landed a rocket, and it's only attempting the first stage so far.