A hashtag is a word or phrase which follows a pound sign (#). This pound sign is also known as a hash. So, when we add # before a word, it becomes a hashtag. It is used to highlight posts on social media. It is a type of metadata that allows you tag content on social sites like Facebook, Instagram, Twitter, and more.
A hashtag becomes a clickable link when you tweet it and anyone who clicks this can see the most recent tweets that contain this hashtag. Thus, it allows you to share posts and engage in online conversations on a large scale. As there is a limit to the length of a Tweet, a hashtag should have a single or few words or few letters.
It is generally used before a keyword or phrase in the Tweet to categorize Tweets by keyword or phrase and increase their visibility in Twitter search. When you click on a hashtagged word in any message, you can also see the other Tweets that contain this hashtag. You can put hashtag anywhere in your Tweet.
Users create hashtags; they are not generated by social media sites. A hashtag becomes popular due to public opinion and engagements, and it changes a word into a link that makes the word easier to find and follow a conversation about that topic. A hashtag can be funny or serious and long or short. It can contain numbers, letters, underscores, and it is not case sensitive. However, we cannot use spaces and punctuation marks in hashtags.
For example: If you want to post a tweet about an event, you can hashtag it with the event name. It will make it easier for people to find tweets related to the event using the Twitter search feature. There a lots of others things for which you can use hashtags, e.g., the hashtag #MeToo points out the incidences of sexual harassment, whereas some others like #OscarsSoWhite shows the lack of diversity in entertainment.