Why do people put "# then a word after it" on Twitter? Why dont they just say the word without the hash key?

[gm14]

?

[The Drunken Fool]

Because it identifies it specifically as a Hashtag.

[Sami]

because its better

[comspec]

The word followed by # becomes click-able tag enabling other users to click & search other tweets with same tag.

[tb]

For trending topics such as #LadyGagasPenis

[Callum Weller]

tags it It links it to the subject

[jd1979]

If you hover your mouse cursor over one of the hashtagged (#) words, you'll notice that putting the Hashtag on it hyperlinks it into a clickable keyword, so that it can be found by people looking for recently posted twitter messages.

So for instance if you've got a fishing blog or fishing website, and you want to inform people of it's existance or of a recent update, you can stick up a note about it through twitter, and the hash tagged keyword such as #fishing or #angling virtually guarantees people looking for tweets on that subject will see it and hopefully check it out.

Or if you want to inform people of a local event you're organising, such as a charity disco or whatever, putting hash tags such as #charity #disco (or similar relevant keywords) + the town you're holding it in (e.g. #Middlesbrough or #Whitby or #York or whatever) with a link to a webpage about it helps ensure it gets found.

Or if you're forwarding a link to a news story, say for instance a report / article on how the Labour knackered the country with mass immigration, using hashtags such as #Labour + #immigration helps it get seen by more people and thus hopefully helps drop Ed's #Millipede + #Balls-up right in it.

Also if you've got a question for the BBC's "Question Time" politics show, you can post it through twitter and get it seen by using the hashtag #bbcqt
Or for the BBC F1 post race forum on the red button, you can send in questions & comments by adding #bbcf1 to your twitter posts.