Ready to wear, known as "pret a porter" in French, is a fashion industry term that signifies that an article of clothing was mass-manufactured in standardized sizes and sold in finished condition—rather than designed and sewn for one particular person. Most of the clothing that we will buy in our lifetime—from sweatshirts to denim, cardigans to handbags—is ready-to-wear, which means it was purchased “off the rack".

Source: Master Class