You are correct! It's not a usual name for a porn site. In fact, it's pretty unusual! I don't know where the E comes and I don't know what those numbers mean. I will not contact the authors to ask them these details. You wanna know why? Cause they do not deserve to be bothered, since they have done such a good job with the actual platform. Yeah, yeah, the layout can be a little confusing for you, but you will learn your way around very fast! E621 will give you hentai, drawings and all sorts of good stuff, when it comes to porn cartoons. Their trending tags are hi-res, mammal, anthro, female, clothing, solo, hair, open mouth, nude, nipples, blush, canine and so many others. You will have the full list in the sidebar! But, how do you get there?
When you will set your foot on the landing page of e621, you will have a search function box located on a big mascot. This is how the site starts! It's good, because you can proceed very fast with your keywords, if you want to look for specific content. If not, see the menu that can be found above the search box. It has buttons for posts, comments, tags (the full list) and a forum which holds the community. It seems that, currently, at the moment of this review, the site is sharing over 1 million posts. Imagine how many will be in the future, since they are doing regular (if not daily) updates.
Let's see what we can have, if we push the Posts button. Voila! It's the sidebar I was telling you about. That's where you can, once again, approach specific content. Next to every tag, you will see some numbers. Those will tell you how many posts have been made under each of them. Nice, ha? There are many other ways to surf the actual content. For example, you can browse by hitting the Artists button. Or Popular, Random, the fuck. So many cartoons, so many sorting options, so much fun!
You understand now why I have said that the authors should not be bothered? Let them concentrate on their work! And let them have their peace of mind, since they fucking earned it with this site called e621. Now you should see it with your own little eyes! Click the screenshot!