What is the difference between a direct message and a mention on Twitter?

[Lydz]

What is the difference between
@something
#something
and a direct message, what do they all mean and how do you do it?

[Jasper]

@username + message --> directs a twitter at another person, and causes your twitter to save in their "replies" tab.
Example: @meangrape I love that song too!

#something --> A hashtag is similar to other web tags- it helps add tweets to a category.
Example: Follow these great people. @jessica, @jasperong and @guykawasaki #ff

D username + message --> sends a person a private message that goes to their device, and saves in their web archive.
Example: D krissy want to pick a Jamba Juice for me while you're there?

[Andrew Z]

Well,

@somepeople in the status will autolink to the twitter with username "somepeople". Just type this in the update box

#something is a hashtag, http://hashtags.org/ , it's like a tag of your tweet, that makes it's easy to join some conversion, like #iphone means it's iphone talk. Just type this in the update box

direct message is private(the status is public), only between you and your receiver, and you can only send message to the people that follows you. Type D someuser your msg