Glossary

The vocabulary of modern backup.

Thirty terms that show up across macup — defined in plain language, with examples. Jump to a letter, or browse the whole set.

Browse terms ↓

A

AES-256The 256-bit variant of the Advanced Encryption Standard, the modern default cipher

B

Backup engineThe layer that owns chunking, dedup, encryption, the repository format, and retention.Backup setA named group of folders and rules that define what a single backup job protects.Bare-metal restoreRebuilding an entire Mac from scratch onto new or wiped hardware.

C

ChecksumA short fingerprint of a chunk of data — any change to the data changes the fingerprint.ChunkingSplitting files into variable-sized blocks so small edits move kilobytes, not gigabytes.Cold storageArchival storage — cheap to keep, slow and sometimes costly to retrieve from.Cryptographic hashA one-way function that turns any input into a fixed-size fingerprint

D

DeduplicationStoring each unique block of data once, however many files or snapshots reference it.

E

End-to-end encryptionData is encrypted on the sender's device and only decrypted on the receiver's

F

File system events (FSEvents)macOS's kernel-level API that tells apps which directories changed, and when Full Disk Access (FDA)macOS privilege that lets an app read files outside its normal sandboxed reach

G

Granular restorePulling back one file, folder, or version — without touching anything else.

H

Hot storageStorage optimized for fast, frequent access — data you might need to restore today.

I

Incremental backupA backup that only uploads blocks that have changed since the previous snapshot.

K

Key derivationTurning a human passphrase into a strong cryptographic key using a slow, salted function KeychainmacOS's built-in encrypted credential store for passwords, keys, and secrets

N

NotarizationApple's automated malware scan for Mac apps distributed outside the App Store

O

Object LockA storage-level rule that prevents objects from being altered or deleted for a set period.

P

PruningReclaiming space by deleting chunks no surviving snapshot still points at.

R

RansomwareMalware that encrypts your files and demands payment for the decryption key Recovery point objective (RPO)How much recent work you can afford to lose — the age of your newest backup.Recovery time objective (RTO)How long you can afford to be down before a restore has to be finished.RepositoryThe encrypted store on a destination that holds chunks, manifests, and snapshot history.Retention policyThe rules that decide which snapshots to keep and which to let go over time.

S

S3-compatibleStorage that speaks the AWS S3 API — interchangeable with S3 at the protocol level.SHA-256A 256-bit cryptographic hash from the SHA-2 family, standardised in FIPS 180-4 SnapshotA point-in-time record of a backup set — every file exactly as it was at that moment.

V

VerificationRe-reading stored backup data and proving, byte by byte, that it is still intact.

Z

Zero-knowledgeA system where the provider cannot read your data, even if compelled to try

Why we wrote this

The vocabulary matters.

Most backup vendors obscure what their product actually does. If you don't know what a snapshot is, you can't tell whether you have one. If you don't know what zero-knowledge means, you can't tell whether your provider could read your files. We publish this glossary because the language is the shape of the product — and you deserve to read it without the jargon.

The words are the easy part.

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