The term "sterling silver" is primarily used in relation to silver, and for such metal to be called as such, it must have a minimum degree of purity, which is established by law in Spain and most EU countries.
In this specific case, regarding the term 925 sterling silver, that 3-digit number signifies the amount of precious metal in a piece. For example, if it's a 925 silver earring, it means that 92.5% is that precious metal, and the rest is another metal.
Earring dimensions: 20mm length, 9.5mm width, and the section measures 0.7mm