What is the meaning of # in URL and how can I use that?

Question

I often found some URL which looks like the following:

www.something.com/some_page/#someword 

After writing this page some_page will be open and then scroll will be set so that I can see that "someword" at beginning of my screen.

I don't know what the meaning of "#" is. As soon as I make #someotherword with any URL it works sometimes and sometimes it doesn't.

I am not getting what # is in the URL. Is it any functionality of any language or URL or something else?

It might be possible that you consider my question newbish, but I am not into web-designing technologies, I am simply curious about it.

I am not the owner of some website, but when I am concerned with some particular portion of some web page then how can I give the URL with # and give that URL to another?

I am concerned with the answer portion on my profile, and then I will prepare the URL just below and will give it to somebody.

https://stackoverflow.com/users/775964/mr-32#answers

This works, but some time it doesn't.

https://stackoverflow.com/users/775964/mr-32#tags

That doesn't work.

I am just a user and I don't want to know in which language the website is build.

Answer 1

Originally it was used as an anchor to jump to an element with the same name/id.

However, nowadays it's usually used with AJAX-based pages since changing the hash can be detected using JavaScript and allows you to use the back/forward button without actually triggering a full page reload.