I was wondering what exactly does X-foot cube mean in a spells range description.
Let's look Thunderwave for example. It says:
A wave of thunderous force sweeps out from you. Each creature in a 15-foot cube originating from you must make a Constitution saving throw.
We took that to mean, all points a square 15 feet from the caster. Or does it mean a 15×15 foot square with the caster in the middle?
Let P be the player and X a 5 foot block that the spell affects.
We decided it to be: Or is it Really: