It originates from the very early days of Open Tibia, before there were any websites for the servers. You all shared the same account (111111/tibia I believe it was?) and could only pick between three characters, Hurz (knight), Hurzel (paladin) and Hurzine (mage). Eventually custom accounts came along, but they had to be created manually by the server admin through the database. It wasn't as fluid as it is today, and someone decided to create a single-page website where you could enter your account number, password and character details. There was literally nothing else to it, that was it, and at that time, this was a lot more dynamic than having to manually create it all through the database. So the term 'automatic account creator' (whether it was given by the person who released it or not I can't recall) was justified. Today, they are more of frameworks/CMS's than an AAC, but I suppose it just stuck around because of nostalgic reasons.