It means data that has been recorded to your health app - steps per day/hour, sleep hours/analysis, heart rate readings if you have a watch or device that does that, estimated calories burned, etc.

Useful data for you to know and control, but incredibly creepy for a corporation like Meta to take for no reason other than to build an intrusive ad profile.

I'm guessing they record if you've been viewing a lot of, say, heartburn-related content, or once said "I suffer from heartburn".

I'm guessing there's no direct place for it there without reading email ( but even then your doctor should not be emailing you directly without a layer of encryption).

Probably it's more of a "hey if we stumble on it it's ours now". Like if you subscribe to a lot of parkinson's info they probably can safely assume you or someone you know has Parkinson's. And they'll use that to shove ads in your face.

These are primarily the data stored by your health apps and sos information.

If you've Android health info stored for emergency cases, some apps with right permission can access it. You know to save your life.

Likewise, your health record on your health apps like Google/Apple/Samsung health store a lot of information about you like steps, sleep trends, heart rate, diabetes, water intake, and even period regularity.

In normal cases these records should only be known to you or shared with apps you approve.

Threads has no business normally to request these data, but if they want go serve you relevant ads, these become quite useful information.

They can show you sanitary products when you're on period, or show ads for meds when you've high blood pressure. None of these should be monetised, but they can very well will be.