A spell which has a verbal spell component is one that requires some form of spoken incantation in order to cast properly.

The spellcaster must be able to speak in a strong voice and if this is hampered they may not be able to use verbal spells effectively.

The spell silence prevents any spell with a verbal component from being cast.

Spells cast using the silent spell metamagic no longer have to fulfill the verbal component requirement.

A spellcaster who has been deafened has a 20% chance to spoil any spell with a verbal component that he or she tries to cast.