In finance or when buying things, off the shelf refers to products that have already been designed and made, compared to "made to measure," (or "one-off," "custom-built," "custom made," etc.), which refers to products that have to be made to a special order. Off-the-shelf products are generally cheaper and more quickly available than made to measure. In the manufacturing of clothing, equivalent terms are off the rack, ready-to-wear, and prêt-à-porter. In computer science, off-the-shelf software is available as a stock item, i.e., not specially designed or custom-made.
