ASP.NET Authorization what does the * and ? mean?

In ASP.NET I often see (and have copied the following) but never really understood the difference between the * and ? symbols.

for example

<system.web>
  <authorization>
    <deny users="*" />
    <deny users="?" />
  </authorization>
</system.web>

Just wondering if anyone can tell me the difference?

Cheers.

From stackoverflow

• ? means anonymous users.

  * means all users.

• The * is a wildcard meaning "everyone", ? means anonymous users.