I used to write my internal HTML links like <a href="dir1/dir2/image.jpg"> and it works.

In CSS, I see it done like url(../dir1/dir2/image.jpg) and it works.

So I had no questions about it.

Recently I am doing some .htaccess URL rewriting stuff and I bumped into problems. With some rewrite rules, stylesheets and images do not get loaded from the index.php unless I prefix their locations with ../
This in turn breaks their paths with different rewrite rules.

So in general and out of my specific context, what does ../ mean for the URL? And how does that affecting when developing locally and for the server?