A hashtag is an in-text label that classifies content into a specific category, first popularized by Twitter users and now common in social media.
A hashtag is a hash sign (#
) followed by a string which is usually alphanumeric, without spaces, punctuation or capitalization. It is used to classify the text in which it is contained and allow searching for related content.
Because of its adoption and usage by a large user base, it has been used in the filtering, searching and sorting of tweets and posts on other supporting social media platforms.
Examples
#StackOverflow
#StackExchange
#1337code