The term "sterling silver" is mainly used in reference to silver, and for said metal to be called as such, it must have a minimum degree of purity, which is what the law establishes in Spain and in most EU countries.
In this specific case, regarding the term 925 sterling silver, that 3-digit number indicates the amount of precious metal in a piece. For example, if it is a 925 silver earring, it means that 92.5% is of that precious metal, and the rest is another metal.
Earring measurements: 17mm long, 8mm wide, and the section measures 0.7mm.