18/0 and 18/10 refer to materials added to the steel to protect the cutlery from rust and the effects of acids in foods and cleaning products.
18/10 is the finest quality stainless steel available. 18/10 stainless steel contains 18% Chrome and 10% Nickel.
18/0 cutlery contains no Nickel and hence it has a lower level of protection. The cost of additional Nickel is reflected in the cost of the product and also in the available guarantee, which tends to be much greater with 18/10 products.