What process does permanent waving refer to in hair treatments?

Permanent waving refers to the process of chemically rearranging straight hair into a curly form. This technique utilizes specific chemical solutions to break down the disulfide bonds in the hair's structure, allowing it to be reshaped into curls or waves. Once the curls are set, a neutralizer is applied to reform the disulfide bonds in their new configuration, resulting in a long-lasting curl pattern.

This process is distinct from other techniques like flattening straight hair, which involves smoothing the hair cuticle, or applying temporary curls using heat, where no chemical change occurs. Highlighting is also unrelated as it involves the application of color, rather than changing the hair's texture. Hence, the definition of permanent waving is correctly identified as the chemical rearrangement of hair to achieve curls.