what does hash tag mean?

[Howard]

[GeneL]

If you have been on Twitter, you may have seen a "hashtag"--->>> #hashtab.

To put it simply, a hash tag is simply a way for people to search for tweets that have a common topic and to begin a conversation.

For example, if you search on #LOST (or #Lost or #lost, because it's not case-sensitive), you'll get a list of tweets related to the TV show. What you won't get are tweets that say "I lost my wallet yesterday" because "lost" isn't preceded by the hash tag.

MORE:
http://contests.about.com/od/g/g/hashtagsdefinition.htm

[Emiliano]

Is a trend in real time.

For example: #PopeFrancisco

[SUDHAKAR Kuruvada]

A HASHTAG is a word or a phrase prefixed with the symbol #.It is a form of metadata tag. Short messages on microblogging and social networking services such as Twitter, Tout, identi.ca, Tumblr, Instagram, Flickr, Google+ or Facebook may be tagged by putting "#" before important words, as in: