Can you tell me what a "hashtag" is or what it is for?

[aspenkdp2003]

I want to know how to use a hashtag or if I need to use it or when to use it...

[Rohan]

Assalam-o-alaikum!
.
Hashtag is a word or a phrase prefixed with the symbol #. It is a form of metadata tag. Short messages on social networking services such as Twitter or Facebook may be tagged by putting "#" before important words, which makes them BLUE and MORE VISIBLE as in:
I found this answer from #yahooanswers.
You may try that on facebook!
-RH

[Dora]

The # symbol, called a hashtag, is used to mark keywords or topics in a Tweet. Hashtags' popularity grew concurrently with the rise and popularity of Twitter.