Gauge refers to the thickness of the metal used to forge or press the utensils. I see some people are confusing gauge with composition which is normally expressed as the ratio of the 2 types of metal added to the steel in the flatware (ie. 1810, 18/10). I have also seen some people incorrectly stating that the nickel is for lustre... that is only 1 function, it is mainly for corrosion resistance and HARDNESS. ANY metal will polish up nicely.
COMPOSITION (aka GRADE): In order to be called stainless steel, a steel alloy must contain at least 11.5% chromium. 18/10 is the highest quality, it contains 18 percent chromium, and 10 percent nickel.
Chromium makes the metal rust proof and stain resistant, while the nickel provides some additional corrosion resistance and makes the metal hard. The rest is composite steel, which makes the utensils strong. 18/8 stainless steel is normally less expensive and has slightly less corrosion resistance. Really though, it's probably not very noticeable. I have recently seen 18/0 since the world supply of nickel is rather low lately. I would not recommend getting these as they will not hold up well & may even look rather cheap after a few rounds through the dishwasher.
GAUGE: Gauge is a measure of thickness, generally from 1 to 4 millimeters, and often determines weight and price of the set. Gauge can be compared by looking at pieces of flatware from the side.
Not all utensils in the same set will have the same gauge... the dinner fork should have a thicker gauge and the salad fork a thinner gauge. The butter knife should have a thicker gauge than all of the other utensils. The gauge imparts strength to the utensil, but it also affects the balance & feel of the utensil in your hand. Good flatware should feel balanced in your hand and feel comfortable whether you are cutting, lifting or piercing food. The gauge reflected on the packaging is generally the average gauge of the utensils. Some more unscrupulous companies my label the package with the thickest gauge piece in the package....