Definition
A cutting line is the outermost line of a pattern piece, the line you cut along, which includes the seam allowance when the pattern provides one.
On a pattern with included seam allowances, the cutting line sits outside the stitching line by the width of the allowance, often 1.5 cm (5/8 in) for wovens. On a pattern without allowances, the outline is the stitching line, and you draw a new cutting line around it before cutting.
Multi-size patterns print a cutting line for each size, each with its own line style or color: solid, dashed, dotted, or with small symbols. Find your size in the key and highlight its line before tracing or cutting, and blend between sizes at the waist or hip if your measurements fall in different ones (see nested sizes). A pattern drafted for one person's measurements has a single cutting line per piece.
Accuracy matters more than it seems. Cutting 2 mm outside the line on every side edge of a skirt adds almost 1 cm (3/8 in) to its circumference. Cut through the middle of a printed line, keep the lower blade of your scissors on the table, and use long, smooth cuts. With a rotary cutter, run it along a ruler on straight edges.
Notches are cut on the cutting line, as small snips into the allowance or tiny triangles outward. Grainlines, darts and dots lie inside the line and are transferred with chalk or a tracing wheel.