红酒 (hóngjiǔ) is a noun meaning "red wine." It is used when talking about alcoholic beverages, dining, or making comparisons involving color and flavor.
晚饭的时候我们开了一瓶红酒庆祝。
Wǎnfàn de shíhou wǒmen kāi le yì píng hóngjiǔ qìngzhù.
At dinner, we opened a bottle of red wine to celebrate.
你喜欢喝红酒还是白酒?
Nǐ xǐhuān hē hóngjiǔ háishi báijiǔ?
Do you prefer red wine or baijiu?
这家餐厅的红酒种类特别多。
Zhè jiā cāntīng de hóngjiǔ zhǒnglèi tèbié duō.
This restaurant has an especially wide selection of red wines.