First-party data is information collected directly by a business from its own customers, users, or website visitors, through channels it owns — such as its website, app, or email list — rather than purchased or shared by an outside company.
This distinguishes it from third-party data, typically aggregated and sold by data brokers with no direct relationship to the individuals involved, and from second-party data, which is another company's first-party data shared through a partnership. First-party data is generally considered more accurate and privacy-compliant because it comes with a direct relationship between the business and the person it describes.
A website's own analytics tool recording that a visitor came from a search engine and viewed three pages is first-party data, while an ad network's record of that same visitor's browsing habits across dozens of unrelated websites is third-party data.
Browsers have progressively restricted or blocked third-party cookies, and privacy regulations increasingly limit data sharing between companies, making data collected directly by a business about its own audience more reliable and durable.
Only if it's collected and processed by the site owner (or a processor acting on their behalf) without being shared with or resold to unrelated third parties — routing it through a large ad-tech network can blur that line.
First-party data is observed from user behavior, like pages visited; zero-party data is information a user deliberately and proactively shares, like preferences stated in a survey or account settings.