sharepoint - What does the vertical line character mean in powershell? -

i using script here

http://blog.kuppens-switsers.net/sharepoint/finding-cewps-with-script-in-your-sharepoint-sites/

and there specific part of script don't understand. in part

   # libraries , lists have views , forms can contain webparts... let's them    $lists = $web.getlistsoftype("documentlibrary") | ? {$_.iscatalog -eq $false} 

what | ? {$_.iscatalog -eq $false} mean? , if possible know why person chose check document libraries?

what point of script is, scans content editor web parts , checks if contents have script tags.

thanks

powershell heavily relies on concept of pipeline. execute command returns collection of objects , pipe command it.

| known pipe character or pipe operator used connect various parts of pipeline.

in case, documentlibraries in sharepoint website , pipe (pass) them where-object cmdlet (? short) apply filter. result assign variable.