Pure Silver is too soft for use as jewelry. So, what jewelers do is mix a combination of 92.5% Sterling Silver and some other component (7.5%) to make a sturdy base for jewelry that lasts. Hence the term 925 Sterling.
The part the consumer should be concerned with is the 7.5% that is not Sterling Silver. It should be copper for maximum benefit but, some disreputable manufacturers will use nickel. With so many folks allergic to nickel, this can be a problem for the consumer.
All of our 925 Sterling is lead and nickel free. Many of our 925 Items are also plated with Rhodium to protect the 925 from turning.