Summarize this article in one sentence.
A hashtag is a word or phrase constructed after a pound sign (#). Hashtags serve to categorize a post so that when a site use clicks on or searches for your specific hashtag, they can view any posts associated with the tag. For example, taking a picture of your food and writing "#meatloaf" would potentially add your photo to your chosen website's collection of meatloaf-based posts. When you add a hashtag to a post, other people will be able to see that post if they search for that hashtag. This means that finding often-searched hashtags and using them in related posts will likely increase the number of people who can interact with that post. Since hashtags serve the same purpose on every site that supports them, using them becomes a matter of choice of website rather than function. Some popular sites include the following:  Twitter Instagram Facebook Tumblr Pinterest Google+ YouTube TikTok Some possible uses include the following:   Marketing - Use your brand name, catch-phrase, or a product's name (or all three) as hashtags to promote a marketing post.  Joining a trend - If your favorite social media platform has a public dialogue based around a trend, adding your opinion with the trend's hashtag (e.g., "#election") will give you a chance to have your voice heard.  Increasing post audience - As mentioned previously, hashtags increase the likelihood that people you don't know will see your post. Especially on Instagram, adding hashtags to your posts will increase the number of people who "like" or comment on them.

Summary:
Know what a hashtag is. Understand what a hashtag does. Make a list of sites on which you can use hashtags. Consider your own reasons for wanting to hashtag.