This type of construction has been part of PowerShell since the very beginning:
Get-Process | where {$_.Handles -gt 500}
Get some data and use where-object to filter the data based on the value of some property. $_ represents the object on the pipeline.
PowerShell 3.0 introduced a simpler syntax
Get-Process | where Handles -gt 500
which is shorthand for
Get-Process | where -Property Handles -gt -Value 500
At which point it becomes obvious what is happening – you are comparing a property against a value. There are a whole set of comparison operators you can use in this manner – see the help file for details.
This new syntax makes life much easier when you only have a single comparison to perform – you need to use the old style syntax if you need to test on two properties.
The problem is that I don’t see this syntax being used that much. If you are using PowerShell 3.0 or above I recommend changing to the new style syntax. It does save typing.