A single RuneScape account gets you access to two versions of the game, each with their own separate character profiles. Handy if you ever feel like a change of pace, scenery, or game modes.
The game you've grown up with over the years. If you haven't played in a couple of years, this is where you'll be reunited with your old profile and items.
Old School RuneScape
Launched in 2013, this backup version of RuneScape from 2007 has evolved into something completely new and requires you start your character from scratch.
Profile progress is completely independent, meaning that character information, stats, and items do not transfer between the two games.