I googled "derail thread". http://www.urbandictionary.com/define.php?term=derailing%20a%20thread http://www.urbandictionary.com/define.php?term=derailing%20a..

I googled "derail thread". http://www.urbandictionary.com/define.php?term=derailing%20a%20thread http://www.urbandictionary.com/define.php?term=derailing%20a... The act of throwing a thread in a discussion forum off topic, oftentimes so much so that the original discussion is unable to continue.