What are the differences between subdomain, parked domain and addon domain?

Subdomain * Let's say your domain is mysite.com. * You install a Message Board and put in in a directory called mysite.com/board/. * You can turn the directory board into a sub-domain by adding it as a sub-domain from your Control Panel. * Now you can access your Message board as either mysite.com/board OR board.mysite.com * This costs ...