What Are Hashtags (#)? I see them all the time on Twitter and Instagram.
Definition: The # symbol, called a hashtag, is used to mark keywords or topics in a Tweet. The hashtag system was created organically by Twitter users as a way to categorize messages.
Hashtags: Help you find interesting Tweets
People use the hashtag symbol # before relevant keywords in their Tweet to categorize those Tweets to show more easily in Twitter Search.
Clicking on a hashtagged word in any message shows you all other Tweets in that category.
Hashtags can occur anywhere in the Tweet.
Hashtagged words that become very popular are often Trending Topics. A hashtagged word in a tweet normally looks like this #movies
Using hashtags
If you Tweet with a hashtag on a public account, anyone who does a search for that hashtag may find your Tweet.
Twitter best practices recommend using no more than 3 hashtags per Tweet, and they should be relevant to the tweet topic