The apps a user has installed on their phone.
Facebook promised users of its new Study app that it would be transparent about the information it collects and that the app would be secure. The company has also restricted the release of the app to two of its biggest markets - India and the US.
Not everyone can sign up to the system - Facebook is running ads for the program, and if you see one you can register with your information, after which Facebook will choose which applicants are eligible to download the app.
If you've got the app downloaded, Facebook will monitor which apps you have installed on your phone, how long you spend on each one, what you're doing in the apps, and where you're based.
Facebook says that the program is created to help it to "learn which apps people value and how they're used" so that the company can "build better products for the Facebook community".
The company's product manager, Sagee Ben-Zedeff, assured users that Facebook won't sell any of the data to third parties, or use it for ad targeting.
Anyone in the US or India who are 18 or older can sign up for the new Study app.
"Study from Facebook" is now only an option for users in the United States and in India who are above 18 years of age.
This time around, it looks like it will only be available to people aged 18 and above, rather than the 13-25 age window from before.
Moreover, media reports also claimed that Facebook even asked users to screenshot their Amazon order history pages.
The user's country, device and network type.
Remember when it was revealed in January that Facebook used to pay teens and gather mobile app usage data from them through an app?
"Approaching market research in a responsible way is really important".
The move also comes at a time when there are global concerns around data privacy and how some of the world's top internet companies had been illegally harvesting user information without taking subscribers' consent.
"Providing users this up front sort of notice is definitely a good thing, and should be the norm for any company which markets, advertises or otherwise makes use of users' personal information for generating revenue", said Nathan Wenzler, the senior director of cybersecurity at wealth management firm Moss Adams.