Hashtag

What is a Hashtag on Social Media?

A hashtag is something like #HappyNewYear, it's a way to categorize posts on social media by including a text code in the body of the post that starts with an octothorpe (#) character (also called a "hash" or "number sign") and contains the name of the category without spaces.

What are hashtags Used for?

On social media that support hashtags, it's generally possible to search for all posts on the platform that contain a specific hashtag. In some cases, hashtags are used to keep track of "trending topics," which are only really useful when lots of posts are posted with a specific hashtag.

Most people don't use hashtags to categorize their posts, so it's hard to find posts by hashtag. You can't expect, for example, that someone who posts a photo of a cat will have the capacity of writing #cat on the post.

Those who do use hashtags may spam every hashtag they know under every post even it's irrelevant to that specific post.

Modern websites can search posts by text anywhere on the post, making hashtags even more irrelevant. Just search for "cat" instead of going to the cat hashtag.

Hashtags do provide some unique functionality. For example, some use the hashtag #FollowBack to announce that they will follow back anyone who follows them, creating a "gain followers quick" scheme. Although most users will not categorize their posts, some users will categorize posts that they want to be easily found on specific topics specially if they know some people are following those hashtags.

Which Social Media Supports Hashtags?

Hashtags are ubiquitous in social media, found on Facebook, Instagram, Twitter, Threads, Bluesky, Mastodon, Youtube, TikTok, and Pinterest.

Exceptionally, Reddit doesn't have hashtags, although it has subreddits, which is in certain ways the same thing.

Observation: Mastodon doesn't have a default algorithmic feed, so new posts made without any hashtags won't be seen by anybody on the social media. This means that without followers you must add a hashtag to everything you post or nobody will ever see it.

Tags vs. Hashtags

Hashtags come from actual post tags that existed in blogs, as social media were originally microblogging platforms. You can still use tags (with spaces) on blogging platforms like Tumblr.

One disadvantage of hashtags compared to traditional tags is that hashtags are part of the post's body, whereas tags are considered metadata. That is, because the hashtag is INSIDE the text, you can't algorithmically replace one hashtag by another in all posts that contain a hashtag because there is no way to guarantee that won't change the meaning of the text.

For example, if a post says "I just downloaded #Krita," you can't change #Krita to #KritaTutorials or #DrawingApps without changing the meaning of the post. However, if a post said "I downloaded Krita," and it had a tag "Krita" associated to it, you could change the tag without changing the content of the post.

This is specially important when you consider that in many cases an user isn't even allowed to modify a post after it has been posted, which means that there is absolutely no way to organize older posts in a new tag structure. Platforms that support tags instead of hashtags, like Tumblr, also provide ways to massively replace which posts are tagged with which tags.

Hashtag Character

Nowadays, hashtag also means the hash (#) character itself. For example, on online text chatrooms such as IRC and Discord, a hash (#) is used before the chatroom's name, e.g. #general for the general chatroom, but some people will call this "hashtag general."

Why Hashtags don't Have Spaces?

Hashtags don't have spaces because the program uses the hash (#) to know where the hashtag starts and a space or the end of a line to know where the hashtag ends. If it could contain spaces, the program would need another method to know where the hashtag ends, like commas (,), but whatever method you use, it's likely to conflict with the normal, non-hashtag text in the post.

This is the same reason why mentions (that use @) generally use usernames and handles that don't have spaces either.