filter square {
    $_ * $_
}

1..10 | square                   # outputs 1, 4, 9, 16, 25, ...
1..10 | % {$_ * $_}              # outputs 1, 4, 9, 16, 25, ...
1..10 | ForEach-Object {$_ * $_} # outputs 1, 4, 9, 16, 25, ...