Which technique is used to create curls in hair?

Creating curls in hair typically involves using a method specifically designed to shape and define the hair into curls or waves. The technique identified in this question, which focuses on curling or waving, directly relates to the tools and methods used for curling. This could involve the use of curling irons, hot rollers, or other styling products specifically designed to manipulate the hair's structure temporarily, resulting in beautiful curls.

In contrast, the other options serve different purposes. Cutting is primarily used for shaping and removing length from hair rather than creating curls. Blow drying can add volume and movement to hair but generally does not create defined curls without the addition of styling techniques or tools. Flat ironing is used for straightening hair and does not create curls, as it flatens the hair shaft.

Thus, the technique that best fits the description for creating curls is indeed curling or waving, as it directly relates to manipulating hair to achieve that specific style.