This answer will serve as a definition of a hashtag in terms of social networking, not mathematically or otherwise.

Hashtags refer to topics—(Especially on twitter.)

On Twitter: It’s this thing where you tweet something and then you use the hashtag (it can be a small phrase or a word) to describe your tweet overall or your thoughts on the subject. Then the hashtag becomes a link to that topic, so that when you press on it it links you to similar tweets with the same hashtags. If a hashtag is overly used on twitter by many users simultaneously it becomes a ‘trending topic’ on your sidebar, and therefore connects all the twitter community to some degree for a few minutes. (Provided you decide to hashtag your tweet as well, although when you click on the link in your sidebar you can still see their tweets)

Apparently many people have taken that concept and applied it to Facebook -it doesn’t work there. It simply has no use on Facebook, that’s why it tends to annoy many, because it implies you’re using them ‘for show’ or without understanding that they really are.

So basically, they act like tags. For instance, on instagram when you post a photo, you use hashtags to tag it so people can view it depending on what topics they’ve added to their profile.

In fact, the idea of ‘adding topics’ to your questions and profiles on Fluther is the same thing.

So technically speaking you are using them correctly to some extent, just not on the right social networking site.

So to answer your question simply: Hashtags are used to add a topic to whatever you are posting. (It doesn’t always have to make sense or relate to what you’re saying.)

Eg.: ‘Yesterday I went to the supermarket to buy some eggs, but upon arriving, I completely forgot why I went in the first place. #lol #whatanidiot #stupidity’ (That’s mainly a twitter thing.)

On Instagram: (Let’s say it’s a picture of a car): #camaro #red #vintage #old
So here’s what you’re doing, you’re trying to link as many people as possible to your photo by adding many subjects so it can be viewed by many.

@Luiveton so my 14 year-old was telling the truth when he said that one cannot use hashtags on Facebook? Several of my digital native friends use them to complement a status so I figured it was ok. Thanks for clearing that up, I thought my kid was just messing with me because he is so horrified that I use social media at all!

To warn me that to read any farther would be a huge waste of my precious time.

POUND SIGN!!!

Yeah.

Not TIC TAC TOE BUTTON (not kidding) like I heard on some stupid phone tree.

Oh lord. People use hashtags on Facebook all the time, to add “a bit of humour” as you say. They only have a legitimate function on Twitter – so either you’re using one device to upload the same status to both Twitter and Facebook (this would make sense), or you’re being a poser. Don’t be a poser. ;)

Often people post their status on Twitter, and have their Twitter posts linked to update onto their FB account.

Plenty of people use hash tags on Facebook. On Twitter, the tag becomes a link that can lead you to other tweets on the same topic. On Facebook, it serves no purpose. It can be funny depending on how it’s used, but it’s already become tiring to see all the random hash tags that really have no meaning. So, yes, your son was correct in a way, but people still do it even though it’s not serving any particular purpose.

Think of Hashtags the same as the Tags we add to our questions here on Fluther. Twitter and Instagram use these to categorize and catalogue related posts. Some people do come up with creative an humorous hashtags, and do so just for fun. Many people cross-post from Twitter and Instagram to their Facebook accounts, so the hashtags will appear, even though the hashtags do not become clickable links on FB, as they do on Twitter or IG, or as the tags do here on Fluther. Also, the ampersand in #George&Weezy will not work on a true hashtag.

On Facebook, sometimes people just use them for fun (which is exactly what I thought you were doing when I saw that status…and I thought it was hilarious!) The kiddos don’t want us to look lame, though. It embarrasses them. :p