Which term refers to methods used to protect against or ward off vampires?

The correct term that refers to methods used to protect against or ward off vampires is apotropaic. This word comes from the Greek "apotropaikos," meaning "to turn away." In the context of vampire folklore, apotropaic practices might include rituals, symbols, or objects believed to have the power to repel evil spirits or beings, such as vampires. Common examples of apotropaic items include garlic, crucifixes, and specific protective spells or prayers.

The other terms do not fit this context. Aeriform pertains to gases, particularly in the context of spirits or entities that are intangible and not directly related to protective practices. Necromantic refers to the practice of necromancy, which is the art of communicating with the dead or raising the dead, rather than defending against supernatural creatures. Chthonic relates to deities or spirits of the underworld, which also doesn't apply to the concept of warding off vampires. Understanding the specific function and meaning of apotropaic methods showcases their cultural significance in various societies' attempts to deal with the fear of vampires and similar entities.