Third-party cookies are small pieces of data stored on a user's device by websites other than the one they are currently visiting. These cookies are created by external services, such as advertisers or social media platforms, to track user behavior across different sites. This tracking helps companies deliver targeted ads and analyze user engagement. Unlike first-party cookies, which are set by the website a user is visiting, third-party cookies can gather information from multiple sites. This capability raises privacy concerns, leading to increased scrutiny and changes in regulations regarding online tracking and data collection practices.