To understand the meaning of a diffusion line we need to find out what is a high-end fashion first.
High-end designs have unique one-of-a-kind styles. They are mostly very expensive and are among the most influential fashion brands. Brands like Chanel, Dolce&Gabbana, Versace, Valentino etc are the best examples of high-end fashion houses. High-end brands are classified by certain features, styles and fabrics. These styles are usually presented to the public on high-fashion runways and mainstream fashion publications and are made of high quality materials from Fashion Boutique. Some high-end designs are custom-made or made-to-order, rather than ready-to-wear garments, which are produced in large amounts with standard sizes.
A diffusion line (or a bridge line) is a secondary line of merchandise created by a high-end fashion house or fashion designer that retails at lower prices. These ranges are separate from a fashion house's "signature line", or principal artistic line, that retails at much higher prices. Diffusion products may be on sale alongside designers' signature line but they can also be made available at concession outlets and certain chain stores. The use of a diffusion line is a part of the brand recognition marketing strategy to reach a wider market in order to increase revenue.
Diffusion ranges serve several purposes for designers. The main are: substantially increase sales volumes as their products become affordable to a wider audience at the lower price point; offset the effect of chain stores copying their products and undercutting the designer's prices.
Let's name some of them: Versace - Versus, Prada - Miu Miu, Marc Jacobs - Marc by Mark Jacobs, Valentino Garavani - RED Valentino, Zac Posen - Zac Zac Posen, Roberto Cavalli - Just Cavalli, BOSS - Hugo, Agent Provocateur - L'Agent, Alexander McQueen - McQ, Donna Karan - DKNY and many others.