What is the blow dryer attachment used to accentuate or keep definition?

The correct choice is the diffuser. A diffuser is a blow dryer attachment designed specifically to spread airflow gently over a larger area without disrupting the natural curl pattern or wave in the hair. This is particularly useful for individuals with curly or wavy hair, as the diffuser helps to reduce frizz and maintain the definition of the curls while allowing them to dry.

The unique design of a diffuser allows it to lift and support the hair at the roots while distributing heat evenly, which prevents excessive movement and maintains shape. This results in a more polished look without sacrificing the bouncy texture that curls provide. Essentially, the diffuser enhances and preserves the styling achieved in curly or wavy hair.

Other types of attachments like concentrators or nozzles have different purposes, such as focusing direct airflow to smooth hair or speed up drying time, but they do not specifically serve to accentuate or maintain the natural definition of textured hair. The term "element" does not apply in this context as it generally refers to the part of the blow dryer that generates heat.