An ounce was a Earth measurement of weight commonly used in the United States of America. One ounce was equal to 1/16th of a pound or roughly 28 grams.
Less than one ounce of antimatter was more powerful than 10,000 cobalt bombs. (TOS: "Obsession")
In 1957, a nineteen ounce can of green beans cost 17¢ at Johnnies Market in Carbon Creek, Pennsylvania, in the United States of America. (ENT: "Carbon Creek")