A diffusion 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 typically retails at much higher prices. Diffusion products may be on sale alongside designers' signature lines 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 strategy of massification where luxury brands attempt to reach a broader market in order to increase revenue and brand recognition.

Derek Lam is an American fashion designer. In addition to designing his own line, Lam was Tod's creative director for ready-to-wear and accessories from 2005 until 2010.