A Twitter hashtag is a way to categorize or add context to a particular Twitter message. Each hashtag is a single word or a phrase with no spaces, preceded by the "#" sign, such as #egypt or #joke. You can use a hashtag to indicate you're participating in an organized chat, such as #seochat, or simply to indicate that your tweet is sarcastic by adding #sarcasm to the end. Search for a hashtag on Twitter search or use a third-party tracking service to find all tweets containing a specific hashtag.
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Log into Twitter.
Compose a new tweet in the "What's Happening?" box.
Type the "#" sign, immediately followed by your desired hashtag keyword or keyword phrase. For example, #apple or #poll. Come up with your own hashtag or use a relevant hashtag that you see in others' tweets.
Click "Tweet" to send your tweet.