The number 800 on silver jewelry refers to the purity of the silver. A majority of silver contains traces of other metals,such as nickel.800 would indicate that your jewelry is 80 percent silver,and 20 percent other metals. The purest silver is stamped .999,meaning trace amounts of other metal are present.
The "800" on your silver jewelry means that it's compounded of 80% silver and 20% of another alloy, usually copper, although nickel was used in some earlier pieces. This grade of silver is inferior to Sterling Silver which is made of at least 92.5% pure silver.
The mark 800 is a mark of the fineness of the sterling silver used in silver jewelry. It can also be used to identify and the maker of the jewelry. The mark is a European mark, and it is used to denote that the piece was made between 1838 to 1961 if made in France.
That means that the piece is only 80% silver, with the other 20% some other metal like nickle. The 800 number comes from 800/1000 hence 80% is real silver.