A fashion line is a clothing subsidiary (usually maintained by a parent company) that designs and sells garments according to a specific ethos, often only slightly different from the company's flagship brand. A single designer or creative director will often be in charge of many lines, each presenting a different take on the company or brand's main idea. A few notable fashion lines include: Abercrombie and Fitch, Aéropostale and American Eagle Outfitters.
Many mainstream brands (Gap, Banana Republic, Brooks Brothers) will use various (sub-)labels to differentiate their more expensive garments from the more common (e.g. Gap's 1964, Brooks' 1818 Collection), but these do not constitute lines per se. A fashion line will have its own retail outlets, design staff, offices, and often, catalogs.