Time To Interactive
"Time to Interactive" (TTI) is a web performance metric that Google used to regard as important, but that has been deprecated by Google in favor of other, more reliant metrics such as Largest Contentful Paint.
The metric is supposed to measure the time it takes for a web page to become fully interactive and responsive. Technically it's measured by the time it takes before getting a 5-second window without long tasks or more than two in-flight GET requests.
The idea behind the metric is that it's not enough to have a page that appears to be fully loaded and ready - we have to make sure that it's actually ready and responding to user input.
Removed in Lighthouse 10
The reason was that the team at Google thought that the TTI metric was too sensitive to outlier network requests and long tasks, so they felt that other metrics such as Largest Contentful Paint and Speed Index were more useful.