Science is our way of finding out how the universe works. We do this by asking questions and then finding facts to enable us to answer those questions. Nature has provided some of the most interesting questions and facts.
Science is how we try to make sense of the world and explore its phenomena. To do so we collect data in a consistent way, and use knowledge that’s already available; we adjust our views as we gather more evidence.
What a awesome question! I would first probably say ‘wow’, cos I just met an alien. Then I would say, ‘when we ask questions about the world and how it works, we try and find out the real answers using Science. It means having an idea, then trying to prove yourself wrong to see if you are right!’
I would say “Science is trying to understand the world around us.”
Interestingly I would probably beam the number pi in binary form. This way if they were intelligent they would figure out that we were too. Any advanced alien would know what pi is (a constant that never changes regardless of where you are in the universe), and binary would be the easiest means of communicating with them!