Human: Can you explain what a "hashtag" is? Assistant: 
A hashtag is a keyword or phrase that is preceded by the "#" symbol and used to identify messages on social media platforms. It can be used to categorize posts, allowing users to search for content related to the topic of discussion. For example, if someone wants to find information about a specific subject, they could use a hashtag like "#history" in their post so that it would show up in searches related to history.