What does notarised mean for a Mac app?
Notarisation is Apple's automated scan of an app before it is distributed outside the App Store. The developer uploads the build, Apple checks it for known malware and for correct signing, and attaches a ticket. macOS checks that ticket on first launch, which is why a notarised app opens without a warning.
Notarisation and signing are two different things
A signature says who built the app and that nobody has altered it since. It comes from a certificate Apple issued to a named developer account, so a signed app has an identity attached that Apple can revoke.
Notarisation says Apple has scanned that signed build and found no known malware. It is automated, it takes minutes, and it is not a review of the app.
Together they are what stops the warning on first launch. An app that is signed but not notarised needs you to open it from the right-click menu the first time. An unsigned app is the one macOS refuses outright without a trip to System Settings.
How we read it
Both come from the code signature on the bundle. Notarisation shows as the ticket attached to the build; the signing identity is the name on the certificate, which is why a listing can tell you the developer account a binary was actually signed by rather than the name on the marketing site.
Those two names differing is not a red flag in itself — it is routine for a studio operating under a company account — but it is the kind of thing worth being able to check.
What it does not mean
Notarised does not mean reviewed, endorsed, or safe. Apple scanned the binary for known malware; nobody looked at what the app does. A notarised app can still be badly behaved, and plenty of unpleasant software has passed notarisation.
Not notarised does not mean dangerous either. Open source software built and distributed by volunteers frequently is not notarised, because notarisation needs a paid Apple developer account. What it does mean is that macOS will make you confirm it, and that you are relying on where you got the app.
A blank means we have not opened the bundle.
Questions
Does notarised mean Apple has approved the app?
No. Notarisation is an automated scan for known malware and correct signing. No person reviews the app, and it says nothing about quality or behaviour. App Store review is a separate and much stricter process.
Why does macOS refuse to open an app it says is from an unidentified developer?
Because the app is unsigned, or signed but not notarised. Gatekeeper blocks it by default. You can open it once from the right-click menu, or allow it in System Settings under Privacy and Security, having decided you trust where it came from.
Is an unnotarised Mac app unsafe?
Not necessarily. Notarisation needs a paid Apple developer account, so plenty of open source software skips it. It does mean macOS has not scanned the build, so what you are trusting is the source you downloaded it from.