What does |% mean in PowerShell

I've come across this today:

$tests = (Get-ChildItem . -Recurse -Name bin |% { Get-ChildItem $_ -Recurse -Filter *.Unit.Tests.dll } |% {  $($_.FullName) })Write-Host ------------- TESTS -----------Write-Host $testsWrite-Host -------------------------------.\tools\xunit\xunit.console.exe $tests -xml test-report.unit.xml

I can't get my head around what '|%' is doing there. Can anyone explain what it used for please?