What is the #(hashtag, pound sign, whatever you want to call it), this # ?

Question

I was browsing through an HTML & CSS site and saw the # sign in quotes inside an anchor <a>. It was something like this:
<a href="#"...and so on>... </a>
Okay, I paraphrased a bit but you get the point, I hope. Sometimes I am not so good at explaining what I meant to explain. Anyway, so I'd greatly appreciate it if someone could help me out by telling me what the # is doing there. I can't come up with anything except maybe just another substitute or filling like the "ipsum dolum no mayo, toasted, no hots"

Answer 1

It's actually called an octothorpe BTW.

https://www.merriam-webster.com/dictionary/octothorpe

Answer 2

They are probably bookmarks:

http://www.hyperlinkcode.com/bookmark.php

https://www.w3schools.com/html/html_links.asp

https://www.w3schools.com/html/tryit.asp?filename=tryhtml_links_bookmark

Answer 3

This # is an OCTOTHORPE, huh? I dunno...I still prefer the basic pound sign which kind of sets my age. I originally called it the busy-signal-maker because they were on the old phones and would do just that. I suppose octothorpe isn't bad. I know it's a million times better than hashtag. Bllyyechh! Ugh! I don't know why but I really hate that word. Hashtag. Ugh. It sounds like a deadly, fungal skin condition. What was my point? Oh, right. No, I had been wondering what it was acting as a placeholder for. I would have asked it no matter what the symbol was, but I appreciate the info. I love learning those weird words that you would, I think almost naturally, think can't possibly have any name...like nobody could ever have bothered to label this...thing. Okay I got one for you. I was in the medical field and it is FILLED with the rarely-known-of so named. The corner of the eye (where, inevitably, everybody's finger goes when "cleaning" or wiping something off the eye. Where the tears drain and cause the symptoms of the sniffles. It is called the Canthus. It is, more specifically the inner Canthus and obviously, the outer corner of each eye is the outer Canthus. What does this have to do with programming? Absolutely nothing. More than absolutely nothing. But, I am one who goes...not on a mild "tangent," no...I am more of an excursion type of guy. With that, my lunch is ready so I shall be back some time. Until then I hope all of you are well.