[He waves a hand in permission, nodding. Zhongli's PULLED SOME SHIT and Childe can't ever look at him the same way again, but that doesn't mean he can't trust him at all. The meticulous care with which Zhongli treats everything isn't likely to have vanished now that the truth is out between them.]

A "phone", it's called. It's a bit like a very fast letter courier--you can send a message directly to another person, as long as they have one of these devices too.

[They could also take pictures with them iirc but Childe's a loser and never used that function so moving on. He watches Zhongli's face as he continues.]

It's also capable of transporting people to other worlds.