Sterling silver is at least 92.5% silver and up to 7.5% other metals, usually copper, and is stamped with either the word "Sterling" or ".925" or the Lion Passant mark. Fine silver (99.99% pure) is generally too soft for producing large functional objects.
Additional meaning of Sterling silver:
The term "Sterling Silver", in reference to the .925 grade of silver, emerged in England by the 13th century.