Final answer:
A guide is a continuous mark used in haircutting to maintain evenness and symmetry, similar to how lines define shapes and shading in drawing.
Step-by-step explanation:
A guide is a thin, continuous mark used as a guide in haircutting. When cutting hair, hairstylists often use a guide to ensure that the haircut is even and symmetrical. Similar to how contour lines define the shape of an object in drawing, such as the outline of a hat on a horseman or the hatching marks that indicate shading and three-dimensionality, a guide in haircutting helps to outline the desired length and shape of the hair being cut. This mark is continuous so that the stylist can keep a consistent length throughout the haircut.