A "925" stamp on a piece of gold jewelry usually has no relationship with the gold but with the silver underneath. A "925" stamp on silver denotes a 925/1000 part purity, or a sample of silver that's 92.5 percent pure.
The "925" imprint means nothing in relation to gold. Gold is not usually assayed at 92.5 percent purity, as this is not a standard value for gold. Gold can be found at 91.7 percent purity, but gold of this purity is usually stamped "22 karat." Many gold pieces that carry a "925" stamp are actually gold plated. The stamping, in this case, relates to the purity of the underlying silver.