The phrase "glass of red wine" refers to a single serving or portion of red wine, typically contained in a glass. Red wine is an alcoholic beverage made from fermented grapes and has been known for its various health benefits such as reducing the risk of heart disease, improving brain function, and promoting longevity when consumed in moderation. A "glass" refers to a standard unit of measurement used for wine or other alcoholic beverages, which typically ranges from 5 to 8 fluid ounces (147-236 ml) depending on the country or region. So, when someone says they had a glass of red wine, it means that they consumed one serving of this drink in a single glass container.