"A nation of shopkeepers" is supposedly what Napoleon called the British. Meant to be a disparaging remark, I doubt if it really matters to people such as Philip Green. A billionaire and owner of a string of retail chains. Yes this country is full of retail but also some of the best run and largest international retail chains in the world.
In basic terms, "retail" refers to the sale of goods to the end user, rather than another business or a government. It covers both bricks-and-mortar shops as well as online stores and estimates put total sales around £300b in 2011. Of this, online sales made up around 10%.
Food and grocery makes up the largest proportion of retails spending (just over 50%) with other major components of the market being clothes, electronics and entertainment.
Retail jobs can include store assistants, managers, marketers, window display dressers, HR, finance and area managers. One in ten people work in retail and can be a great learning ground if you wish to ever set up a retail store for yourself.
Because the retail industry is mostly a customer facing role then the kinds of skills and qualities needed are similar to those of many sales roles. You need to be able to build a rapport with a person, enjoy interactions, enjoy helping people, be confident and sound knowledgeable about a product.