Why do I keep seeing this #hashtag everywhere?

Curious about this little symbol #

Simply put, a hashtag is an easy way for people to categorize, find and join conversations on a particular topic and you can use hashtags successfully to promote your brand.

Words or phrases in messages on social networking services such as Facebook, Google+, Instagram or Twitter may be tagged by entering # before them, either as they appear in a sentence or appended to it.

A hashtag allows grouping of similarly tagged messages, and also allows an electronic search to return all messages that contain it. Because of its widespread use, the word, hashtag, was added to the Oxford English Dictionary in June 2014.