A style line is a line or curve in a garment

Clothing

Clothing refers to any covering for the human body that is worn. The wearing of clothing is exclusively a human characteristic and is a feature of nearly all human societies...

 that has a visual effect, e.g., the seam

Seam

Seam may refer to:* Seam , the line where two or more layers of fabric are held together by stitches* Seam , a stratum of coal or mineral that is economically viable; a bed or a distinct layer of vein of rock in other layers of rock...

 between two fabric

Textile

A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...

s of different color

Color

Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

s or textures. For comparison, a nearly invisible seam, such as a dart

Dart (sewing)

Darts are folds sewn into fabric to help provide a three-dimensional shape to a garment. They are frequently used in women's clothing to provide a fit that closely follows the shape of the wearer.Two kinds of darts are common in blouses for women:...

 or pleat

Pleat

A pleat is a type of fold formed by doubling fabric back upon itself and securing it in place. It is commonly used in clothing and upholstery to gather a wide piece of fabric to a narrower circumference....

, would not be considered a style line. A style line is a boundary between two distinguishable areas of fabric, or a visible edge of fabric such as the neckline

Neckline

The neckline is the top edge of a garment that surrounds the neck, especially from the front view. Neckline also refers to the overall line between all the layers of clothing and the neck and shoulders of a person, ignoring the unseen undergarments....

, waistline

Waistline

Waistline refers to:*the waist on a human body — the narrow point of the abdomen between the ribcage and hipsor*Waistline — the line of demarcation between the upper and lower portions of a garment, which notionally corresponds to the natural waist but may vary with fashion from just...

 or hemline

Hemline

The hemline is the line formed by the lower edge of a garment, such as a skirt, dress or coat, measured from the floor.The hemline is perhaps the most variable style line in fashion, changing shape and ranging in height from hip-high to floor-length...

.

As the term is generally used in practice, a style line is introduced only for fashion

Fashion

Fashion, a general term for a currently popular style or practice, especially in clothing, foot wear, or accessories. Fashion references to anything that is the current trend in look and dress up of a person...

 or cosmetic purposes. However, a style line may also fulfill a shaping function as a dart, a seam

Seam (sewing)

In sewing, a seam is the join where two or more layers of fabric, leather, or other materials are held together with stitches. Prior to the invention of the sewing machine, all sewing was done by hand...

at which a dart may end, or as a way of hiding details of the garment's construction.