Design of products, services or environments to ensure they are fit for purpose and meet the intended need or market opportunity and identified criteria for success. Criteria for success in relation to functionality are likely to include such things as operation, performance, safety, reliability and quality. That is, does the product, service or environment do what it was meant to do, or provide what it was meant to provide? (Fork example, does the torch provide light, is it easy to hold, and is it safe to use?)