Which type of cookie is typically used for tracking user activity across multiple sites?

The correct choice, a third-party cookie, is specifically designed for tracking user activity across multiple websites. These cookies are set by a domain other than the one the user is currently visiting. When a user browses the internet and visits various sites that contain content from other domains—like advertisements or social media integrations—those third-party domains can place cookies on the user's device. This allows them to collect data about the user's browsing habits over time, across different websites, which is invaluable for targeted advertising and understanding user behavior.

First-party cookies, in contrast, are set by the website being actively visited and are typically used to enhance user experience on that specific site, such as remembering login information or user preferences. Session cookies are temporary and expire once the browser is closed, making them less useful for long-term tracking across multiple sites. Visitor cookies, while not a standard term in cookie classifications, usually refer to cookies related to user sessions on a particular site rather than cross-site tracking.

Therefore, third-party cookies are the standard for gathering extensive user data across various online platforms, making them essential for marketers and advertisers.