In oracle terminology, what is the difference between an inbound and an outbound oracle?

Inbound = the outside world → the blockchain (e.g. feeding in a price or a sensor reading); outbound = the blockchain → the outside world (e.g. triggering a payment or updating an ERP system). Direction is named from the blockchain's point of view.

Almost all early oracle work — and even an ISO/TC 307 technical report — treats oracles as inbound only: their "sole task" is getting off-chain information onto the chain. That makes sense because the closed-world limitation is most obviously about reading external data. But the reverse matters too: a chain can store state yet cannot actively push it out, so an outbound (also called reverse) oracle is needed to let the outside world act on what the chain now knows. Recognizing outbound as a first-class direction is part of what makes the four-pattern framework complete.