Cursum is a tidally locked planet orbiting the star known to inhabitants as "the Sun" (or often just "the Light"). One side is caught in perpetual light, resulting in a scorching desert, while the other is in perpetual dark, resulting in a frozen wasteland. A thin band around the middle, corresponding to dawn or dusk is habitable to life, and it is in this band that various D&D campaigns occur. Due to the nature of the planet, directions are listed as being "Lightward", "Darkward", "Roundward" and "Counteroundward" (Lightward and Darkward being self explanatory, Roundward travelling with the Light to the right, and Counteroundward the opposite).

Magic is a powerful force upon Cursum. On the planet most magical forces are aligned with being Lightward or Darkward, though a few are associated with Roundward. For example, Lightward is associated with the elements of fire and earth, while Darkward is associated with air and water. Meanwhile, aspects of change, variability or balance, such as life, are usually Roundward. Each sapient creature of Cursum has a true name which can be used in magical rituals to control that creature, usually by binding or harming it. As such many inhabitants of Cursum, especially magic users, use false names.