What with the "#[something]" at the end of message?

[GeneL]

It's called a "hashtag".

The # symbol, called a hashtag, is used to mark keywords or topics in a Tweet. It was created organically by Twitter users as a way to categorize messages.

Using hashtags to categorizing Tweets by keyword:

People use the hashtag symbol # before a relevant keyword or phrase (no spaces) in their Tweet to categorize those Tweets and help them show more easily in Twitter Search.
Clicking on a hashtagged word in any message shows you all other Tweets marked with that keyword..
Hashtags can occur anywhere in the Tweet – at the beginning, middle, or end.
Hashtagged words that become very popular are often Trending Topics.