These are common terms used to describe metals used for jewelry and crafts.

Base metal  ~ Catch-all term in the jewelry industry for metals used in costume jewelry. In metal working, base metal is any metal that is not one the noble or precious metals. The term precious metals usually means platinum, gold or silver. Examples of base metals include iron, steel (an alloy of iron and other metals), copper, brass (an alloy of copper and other metals), nickel, lead and tin.

Gold-Plated, Silver-Plated and Nickel-Plated ~ In costume jewelry, base metals are often plated with a very thin layer of gold, silver, nickel or rhodium. Many plated items are plated first with copper. Many gold-plated items have a white nickel plate under the final gold plate. There is an industry standard of .15 to .25 mils thickness of gold, silver or nickel which is plated to the surface of the base metal (brass, steel ).

Nickel Silver ~ items are made of an alloy, mostly containing nickel, used as a less expensive alternative to sterling silver. Nickel silver resembles sterling silver in color, with a greyer tone.

Sterling Silver ~ items are made of 92-1/2% pure silver and 7-1/2% copper or other alloy, proportions fixed by law (thus the label .925 silver). Sterling silver will 'patina' in time, that is, its color will take on an "antique" look. Sterling Silver contains at least 92.5% silver. The most common sterling alloy is 92.5% silver and 7.5% copper. Tarnish resistant Argentium™ sterling is 1.2% germanium, 6.3% copper and 92.5% silver. Fine silver, sometimes stamped .999, is 99.9% pure silver, which means it is softer and more malleable than sterling. Sterling components and jewelry made in the USA are often stamped "sterling." Goods made for international trade are often marked "925" indicating the 92.5% fineness.  Sterling silver does not have to be stamped to be sterling silver. Items such as chain and small findings are difficult to stamp and the process would increase the cost.

Stainless Steel ~ The generic term for grades of steel that contain more than 10% chromium, with or without other alloying elements. Stainless steel may also have varying additions of nickel, molybdenum, titanium, niobium and other elements. Stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained. The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide. The most common grades of stainless steel are: TYPE 304 - The most common type (chromium-nickel stainless class): accounting for more than half of the stainless steel produced in the world. This grade withstands ordinary corrosion in architecture, is durable in typical food processing environments, and resists most chemicals. Type 304 is available in virtually all product forms and finishes, including jewelry components.  TYPE 316 - Also a chromium-nickel stainless class, 316 contains 2%-3% molybdenum (whereas 304 has none). The inclusion of molybdenum gives 316 greater resistance to various forms of deterioration.

Vermeil ~ items are made of sterling silver, heavily electroplated with 22kt yellow gold.

Pewter  ~ A soft greyish-colored alloy having tin as its chief component. Originally used as an alternative to sterling, prior to the invention of silverplate. Some pewters contain small percentages of lead.

Difference between gold-filled and gold plate: There is a difference between gold-plate and gold-filled. Gold-fill is 50 to 100 times thicker than regular gold-plating, and about 17 to 25 times thicker than heavy gold electroplate. The base metal used is usually brass, copper, or steel. Gold-filled items are made by combining a layer or layers of gold alloy to a base metal (usually brass) then rolling or drawing the metal to the desired thickness and shape. Gold-plate is a very thin deposit of gold, electroplated or electrochemically applied to the piece. (The industry standard is .15 to .25 mils thickness of gold-plated to the surface of the base metal.) It is a very small fraction of an inch thick (1/1000 inch to 1/1,000,000 or so of an inch thick). Heavy gold electroplate might be .002 or .003 inches thick. Gilt is another term used, which means there is a very thin finish of gold color over the base metal (may or may not actually be gold).

Who regulates the Jewelry Industry?  Federal Trade Commission (16 CFR Part 23 Guides for the Jewelry, Precious Metals, and Pewter Industries) found at FTC.gov