What is a hashtag and how is it used?

A hashtag is a word or simple phrase with a hash mark in front of it, used to identify a keyword and facilitate a search for it. To use a hashtag, simply add a "#" sign before a word or phrase without any spaces or punctuations.

As of 2015, hashtags are used commonly in text messages, advertisements, chats, songs and other social media. The hashtag is used to engage with audiences and can also be used to track posts and other valuable marketing information. A number of networks support hashtags, including Twitter, Facebook, Instagram, Google+, Tumblr, Pinterest, YouTube, Kickstarter and Vine.