What does the & symbol in powershell mean?

Question

& is the call operator which allows you to execute a command, a script, or a function.
For more details:
SS64 documentation: Call operator (&)
Microsoft Docs: Call operator &

Syntax
      & "[path] command" [arguments]

Example:

$LocalComputerName = & $ENV:windir\System32\HostName.exe

Also, if you use an IDE (such as PowerGUI) you can block it from opening a separate window when executing a secondary process:

& more
Start-Process "my_script.here"