There's no reliable way to determine if a user is unique. We can check IP address and user agent, but this still may lead to different users being detected as one user - e.g users connected with through one router router will have the same IP address. And as browsers are auto-updated the user agent is not a unique data as well.
The number of sessions combined with TLH (total listening hours) show to a certain degree how popular a radio station is. Also, the average number of simultaneous listeners shows how many people stay tuned in and what time of day (and days of week) are popular.
