Which of the following techniques is generally referred to as a retouch application?

The technique referred to as a retouch application is typically known as a base application. This technique is specifically used to apply color to the new growth area of the hair, ensuring that the hair color remains consistent and vibrant from the roots to the ends. A base application focuses on refreshing the roots of previously colored hair, making it ideal for maintaining a solid color and minimizing visible regrowth.

In contrast, a full-head application involves applying color to the entire head of hair, which is different from retouching the roots alone. A touch-up may sound similar, but it can sometimes refer to smaller corrections rather than the systematic reapplying of color to the growth area. A partial application generally targets only specific sections of hair, rather than the roots overall, making it unsuitable for the definition of a retouch application. Thus, the base application is the most appropriate choice for describing this retouch technique.