The technology used to track user activity on websites for analytics purposes is cookies, specifically HTTP cookies. These small data files, stored on a user's device, collect information about browsing habits, preferences, and interactions with the website. By analyzing this data, website owners can gain insights into user behavior, monitor traffic, and measure the effectiveness of marketing strategies. Additionally, tools like Google Analytics leverage cookies to provide comprehensive reports on site performance, user demographics, and engagement, which can guide informed decisions for enhancing user experience and optimizing content.