In jewelry what does 18K WGP stand for?

18k means the jewellery is made from gold which is 75 % pure. It has other metal blended with it to strenthen it.

WGP = White gold plated

>>>The above is partially correct.

While customers often think the "p" stands for plating, it actually refers to the Word "plumb" - a goldsmiths' term that means the piece is exactly the fineness indicated.

e.g. 14kgp means 14 karat gold, plumb by weight. This means that the jeweler has the ability to fashion alloys with .999 fineness and can test (assay) the exact content of the alloy with precision.

Be aware that a piece of gold jewelry does not have to assay to the exact amount stamped, but just has to come very close to it - three parts per thousand if the piece has no solder (a goldsmiths' metal "glue" which holds parts together) and seven parts per thousand if the piece does contain solder.

That said, there are many unethical jewelers who may tell you otherwise; or attempt to use the misconception to their advantage.

Some jewelers use no fineness stamp at all.

The absence of a stamp (i.e. 14k or 18k) is perfectly legal because the government does not require manufacturers to stamp the amount of gold in a piece of jewelry. If a manufacturer does use a gold mark, federal law requires that it be accurate and accompanied by a maker's mark - either the company's initials or registered trademark. The maker's mark helps in investigation of gold that falls below the mark.