Selfridges is a large British department store. The famous one stands on Oxford Street in London, and there are others in big English cities. Inside you can buy clothes, food, furniture, kitchen things — almost a whole shopping street under one roof, and on the expensive side. People go for the windows at Christmas, for the food hall, and because the name still means 'a smart London shop'. It is a proper name, so it takes a capital S. Though actually it is not a word built from self. It comes from a family name: Harry Selfridge opened the London shop. The -s on the end is like Harrods: part of the shop's name, not a plural you can count. In Taiwan you would treat it the way you treat SOGO or 新光三越 — a store brand, not a vocabulary word about 'yourself'.