Mastering Windows PowerShell Scripting - Third Edition

Comma

The comma operator may be used to separate elements in an array, for example:

$array = 1, 2, 3, 4 

If the comma operator is used before a single value, it creates an array containing one element:

$array = ,1 

When working with functions, the comma operator can be used to emit an array as an object. PowerShell will expand an array by default. The Write-Output command can be used with the NoEnumerate parameter to achieve the same thing.