. (source or dot operator)

When you dot source a script, all variables and functions defined in the script will persist in the shell when the script ends.

Syntax
      . filename [arguments]

Key
   filename    The path and filename of the script to run.

   arguments   Any arguments for the script.

Example

PS C:\> . C:\scripts\myscript.ps1
PS C:\> . ./script64.ps1

#If dogs run free, why not me, Across the swamp of time?, My mind weaves a symphony, And tapestry of rhyme# ~ Bob Dylan

Related:

& (call) - Run a command script
PowerShell Operators - Syntax
Run a PowerShell script - Syntax
Invoke-Item - Invoke an executable or open a file