How is an industry, sector and market defined?

1. An industry is a group of firms producing products and services that are ‘essentially the same / serve the same need. e.g. the airline industry 2. A sector is is a broad industry group. The terms is often used with regard to public service industries 3. A market is a group of customers for specific products or services that are essentially the same (e.g. the market for luxury cars in Germany).