@ on Nostr: What is this ?

{ "id": "5b20d46194da5ee49383ae51a7429b85b4d12895560b1f40e681d29c5d0b300c", "pubkey": "db4787e0b153491da96b764228150f1e2e66c44e245b64a13f8dfd169d5eff3a", "created_at": 1675434547, "kind": 1, "tags": [], "content": "What is this ?", "sig": "07112be17659d223c7ddd83ca9a3a9edf6b7c869665d93a295ac86284195778cd16e2000b2534c3cf68ac6bf087050f67b84d20c08f4d55bc4f4a53fb2013edf" }