A hashtag is a number symbol (#) used to label keywords in a tweet. The name "hashtag" was coined by Twitter and combines the word "hash" (another name for the number symbol) and "tag," since it is used to tag certain words. In order to tag a keyword in a Twitter post, simply type a number symbol (Shift+3) immediately before the word. For example, you can tag the word "tech" in a tweet by typing "#tech."
Twitter automatically turns hashtagged words into links to a dynamic feed. This feed is updated in real-time and lists all recent tweets containing the same hashtag. When you post a tweet with a hashtag, your tweet will show up in the public feed. Besides clicking on hashtags within tweets, you can also search for hashtags using Twitter's search feature.
Hashtags are used to categorize tweets, since all tweets with the same hashtag are related. Therefore, searching for hashtags is a good way to monitor hot topics or trends. For example, #marchmadness is popular during the March NCAA tournament, while #election might be popular during political elections. Company names, such as #apple and #microsoft, are common hashtagged terms and may be used when people comment on new product releases. As people post tweets with the same hashtag, the corresponding feed can easily turn into a discussion.
A hashtag can be any word or combination or words and can also include numbers. You can use trending hashtags in your tweets or make up your own. However, it is best to use popular hashtags if you want others to see your tweet. Each Twitter post can include multiple hashtags, though Twitter discourages spamming tweets with hashtags and recommends using no more than three hashtags per tweet. It is common to include hashtags at the end of a tweet, but you can hashtag any word by simply adding a number symbol in front of it.