what does # mean in Twitter?

[triquetra1754]

I have seen several words proceeded by the # sign. What does it mean in Twitter?

[William W]

Don't know about twitter, but # in math means 'not equal'.

[Windowphobe]

It's a hashtag. What it means is "keyword": the idea is to make all the related tweets searchable by that one word (or string of words).

As I write this, one Trending Topic is #howdareyou; if you have something to say on that topic, just add #howdareyou to your tweet. (It does count toward your 140 characters.)

[Boboo]

keyword are called hashtags. Hashtags are tags that show that a tweet is about a specific topic.
Read the article below for an in-depth explanation.