What are gravitational waves in simple language?

Gravitational waves

A user of the social media platform Reddit was forced to explain to a couple of children (five years old) one of the most important scientific discovery announced, the existence of gravitational waves. As he succeeded to clarify this important achievement to these kids, he decided to share his summary of the facts with other Internet users. Before long, he got a lot of popularity among users and was even praised by one of the scientists who participated in the experiment.

You know how when you throw a rock in a pool, there are ripples? And how if we throw bigger rocks in, they make bigger ripples? Well, a long time ago, a really smart guy named Einstein said that stars and planets and stuff should make ripples in space, and he used some really cool math to explain why he thought that. Lots of people checked the math and agree that he was right. But we’ve never been able to see those ripples before. Now some people built a really sensitive measuring thing that uses lasers to see them, and they just proved that their device works by seeing ripples from a really big splash. So now we know how to see them and we can get better at it, which will help us learn more about space.