s.charSet variable is required for Adobe Analytics implementation for accurate processing of non-ASCII characters. The value of charSet should reflect the character set of the page. If the charSet is not defined or set incorrectly, the non-ASCII characters will be incorrectly shown (unreadable) in the reports.
All modern Adobe Analytics implementations should be supplemented with Adobe Experience Cloud ID (aka Marketing Cloud ID or Visitor ID Service). This replaces the fid parameter with the mid parameter passed in the Adobe Analytics beacon.