Which tool is commonly used for creating curls or waves in hair?

The tool commonly used for creating curls or waves in hair is the curling iron. A curling iron is specifically designed for this purpose, featuring a heated barrel that can be used to wrap sections of hair around it, allowing the heat to enable the hair to take on a curled or waved shape. This is crucial for achieving various types of curls, from loose waves to tight ringlets, depending on the size of the barrel and technique used.

While a flat iron can also be used to create waves through a technique called "bump waving," it is primarily intended for straightening hair. A round brush is primarily used in conjunction with a blow dryer to add volume and shape to the hair during the drying process, but it does not provide the same defined curls that a curling iron does. The blow dryer is essential for drying hair and can be used to create styles with volume, but it does not inherently curl the hair like a curling iron. Thus, the curling iron remains the most appropriate and effective choice for creating curls or waves.