exactly-once processing
Each message has its effect exactly one time, even if it was delivered twice.
Exactly-once processing is at-least-once delivery plus a receiver that ignores duplicates (by message ID) or whose handling is idempotent; the network alone cannot promise it.
Examples
Resend until acknowledged, then have the server skip any sequence number it has already seen: each reading counts once.
"Dose 812: 5 L" can arrive twice, but a device that remembers job 812 runs it only once.