Why do people put '#' in front of words on twitter?

[小花]

[♪D<3]

if you ever find out tell me! haha, i think it's lists?
xo

[Gaz]

usually means number

[James]

It's so topics can be grouped...

If everyone tags #studentprotests, you get everything relating to the student protests that are occurring at the time.

If you simply typed student protests, you wouldn't necessarily get everything related to the student protests.

For example:

By searching "student protests" ...

- You would pick up....
keep up ya silly student protests - layabout #studentprotests

- But not...
i support the #studentprotests

By searching "#studentprotests" - you would get both!

[Lenny Sadiki]

its kinda like a tag or lists or if you wana know more about the subject

[Joanne M]

The hash mark (#) before a word in a post allows you to tag that post for that word. However, in order to get tracked via a hash tag, you need to opt-in and follow http://www.Hashtags.org.
If you then visit Hashtags.org, you can click on any tag and it will show you all of the posts that have been tagged with that keyword.