The format of a retailer is the overall appearance and feel that it presents to customers, primarily its look and layout, the sort of range it stocks and the approach taken to pricing.
Format is distinct from fascia which, strictly speaking, refers solely to external appearance. Retailers occasionally use it as as a synonym for format.
The format, together with range, pricing and marketing, is one of the key determinants of a retailer's success. Of these, the format is very often the hardest to get right. A good format will both draw in customers (generating footfall) and help present products well to generate sales.
Because the format is so important, growth investors can often benefit by identifying smaller retailers who have recently developed formats that are good enough to provide a platform for sustained growth.