What does the term "foil" refer to in the context of hair coloring?

In the context of hair coloring, "foil" specifically pertains to the use of strips of foil that are utilized to separate hair sections during the highlighting process. This technique allows the stylist to apply lightening or coloring products precisely to selected strands of hair while shielding other sections, which helps in creating depth and dimension in the hair color. The foil serves as a barrier that keeps the treated hair separate from the rest, ensuring a controlled application and preventing unwanted transfer of color. This technique is essential for achieving clean, defined highlights or lowlights, which is a desired effect in many hair coloring styles.