Ready to wear is taken from the french "pret-a-porter". It is clothing that is sold in finished condition in standard sizing. Each Fashion designer usually shows both a fall and summer collection in a year, at one of the fashion weeks around the world. It is sold at either the designers flagship stores or at high end departments stores such as Harvey Nichols.
Different design houses produce R-T-W in different ways depending on demand, for example some fashion houses such as Gucci mass produce individual garments based on previous demand and some fashion houses will still only produce a limited amount such as Roberto Cavalli, and once they have sold out of one design there are no more.
In contrast to couture, these lines are never one of a kind. High-end ready-to-wear lines are sometimes based upon a famous gown or pattern that is then duplicated to raise the designer's visibility level and make them able to increase prices.
Ready to wear garments are usually made by machine apart from maybe the odd hand finishing, they are still of very high quality and use high standard fabrics.
A ready to wear designer must remember that the designs of their collections must stay current for 6 months and therefore trends are often taken from R-T-W clothing.
To show the contrast between Couture and R-T-W I have posted pictures of Dior spring summer 2011 ready to wear collection. You will notice they are alot more wearable ... Yet I still wouldn't pop to tesco in one of these fab dresses.