Appearing on the same line as the school and subschool, when applicable, is a descriptor that further categorizes the spell in some way. Some spells have more than one descriptor.
The descriptors are acid, air, chaotic, cold, darkness, death, earth, electricity, evil, fear, fire, force, good, language-dependent, lawful, light, mind-affecting, sonic, and water.
Most of these descriptors have no game effect by themselves, but they govern how the spell interacts with other spells, with special abilities, with unusual creatures, with alignment, and so on.
A language-dependent spell uses intelligible language as a medium for communication. For instance, a cleric's command spell fails if the target can't understand what the cleric says, either because it doesn't understand the language he is speaking or because background noise prevents it from hearing what the cleric says.
A mind-affecting spell works only against creatures with an Intelligence score of 1 or higher.