Bitcão on Nostr: What mean outbox?

{ "id": "fe67f8d6acc913a1347b6a3d3168a0a7b8446e2a7a7686b2ac600d16f660e1ca", "pubkey": "7bbe9e6e5d2c5ec10ab2bdcacc6971710fd2797741f6b283015fc34fe409df44", "created_at": 1727311176, "kind": 1, "tags": [ [ "e", "d423aa132e5dc741ddecbac5e67515b6fd900c2559058397ec7fd860b3d77ea6", "", "root" ], [ "p", "460c25e682fda7832b52d1f22d3d22b3176d972f60dcdc3212ed8c92ef85065c" ] ], "content": "What mean outbox?", "sig": "cb62612dec70df86a83a965fda18a1e2757bdbc40ae9822d8318408533d1e3bb61b5666c64f10115081a20129de4c7e47e7d2b948a5b36ad79ad4b906d99a353" }