People who were signed in on your site when the snippet saw them. The snippet detects this from the session — you do not call an identify function.
One Row Is One Person, Not One Browser
Several anonymous IDs belonging to the same email are merged into a single row. Someone who uses your product on a laptop and a phone appears once, with the activity from both attached.
This is the key difference from the Anonymous list, and it is why the two counts are not comparable — see Why the two lists don't add up.
What Each Row Shows
Who they are, when they were last seen, how many pages and sessions they have, the device and country, and which tracked site the activity came from. Each row also has its own heatmap button that replays that one person's behaviour across every browser they used.