People have only just found out the most famous door knock actually has a name

A man has left social media in shock after revealing that the most famous door knock has a name.

The knock - with five taps followed by a short gap and two more taps - is recognised by many people across the world and while most of us assumed it was just a fun way to let someone know you’re outside, there’s actually a lot of history behind it.

After watching something with the subtitles on, Calum noticed that the knock has its own moniker.

“So, can we talk about the fact that I was today years old when I found out that this knock . . . has a name? What?” He says at the beginning of the clip, which has over 15,400 likes so far.

“I was watching Netflix with the subtitles on, which is a new thing for me. Lots of people do that. Why? Why do you do that?” Calum added.

“Anyway, I’ve started to do it, and someone knocked like that. They knocked like that, and it came up in the subtitles, the name of that knock.”

The big reveal of the door knock’s name was described in the subtitles, which lead to him researching the name to make sure it was legit.

“Apparently, the name of said knock is ‘the shave and a haircut,’” he shared.

He then sings, does the knock on his table while singing along: “ “It’s shave and a haircut, two bits.”

“Two bits back in the day was American for 25 cents, and then in the UK, it was ‘shave and a haircut, five bob,’ which was, I don’t know, shillings, something in shillings,” the TikToker explains.

Clearly in shock, he continues: “Anyway, this has f--king blown my mind. Is this just me? This has blown my actual mind.

“Annoyingly though, the origin isn’t quite clear. Like, I’ve been looking, and I can’t seem to find out how it’s originated. Some are saying Morse code, some are saying, like, it was used in a song in, like, the 1890s. I need to know. I need to know the history.

“Now that I know some of it, now that I know it has a name, I want to know where that name came from, OK? Where has it come from?”

People were just as shocked in the comments. “Mind blown,” someone responded.

“Wow I didn’t know that,” another person commented.

While a third penned: “I didn’t know either.”

The seven-note door knock is also used at the end of a musical performance for comedic effect and is officially known as “Shave and a Haircut”. It was also used in many early cartoons, like Looney Tunes.

The “two bits” – the two knocks at the end – is a reference to 25 cents in the U.S. and Canada, or “five bob” in the UK, which was slang for five shillings.