What is the meaning behind the "Hash tag" #?

[Spazz]

LOL-So as you can tell, I'm not on twitter but I'm always hearing this hash tag thing and comedians even use it in jokes.

So I'm thinking that it's used in front of words so that you can get your post bumped to the top of the list, is this true?

[Nancy Kay]

the hash tag symbol when used next to a word or phrase creates a side-discussion. for instance, I write #lostmymind...when others see it, they can write the same (#lostmymind) and up pops a screen for comments and discussion on that "topic"