When people talk about silver this is usually what they mean. It is the silver standard that has been used in the UK for hundreds of years
By weight Sterling silver is 92.5% silver with the remaining 7.5% other metals, usually copper. In some recipes a percentage of the copper will be replaced by other metals to give the silver certain qualities. In the UK sterling silver items above 7.78g have to be hallmarked at an assay office before they can legally be sold as, or described as silver.
Sterling silver tarnishes due to the reaction of sulphates in the atmosphere with the copper content.