I have just read this, and I am not at all sure I fully understand, best keep off Twitter I say.
What Are Hashtags ("#" Symbols)?
Definition: 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 categorize 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.
Example: In the Tweet below, @eddie included the hashtag #FF. Users created this as shorthand for "Follow Friday," a weekly tradition where users recommend people that others should follow on Twitter. You'll see this on Fridays.