Fast fashion is a method of reproducing high-fashion clothing in large quantities and for low prices. It is "fast" because new styles and trends spend very little time on paper in the design stage, rather, the items are produced and sold right away.
The production of textiles, including making and dyeing them, uses a significant amount of water and energy, which contributes to resource shortages. Wastewater from these processes is often not disposed of properly, polluting the environment. The manufacturing also adds to the amount of microplastics in the ocean, disturbing marine life. The sheer amount of production also leads to unsafe conditions for factory workers.
Fast fashion is generally of lower quality, and new styles replace the old very quickly, resulting in rapid purchase and disposal of clothes. Most fast fashion products end up in the landfill.