To cope with the financial downturn, households are advised to tighten their belts.

tighten 是动词，意思是"收紧、使变紧"，这里指在经济上更加节约。 their 是形容词性物主代词，指代前面提到的 households（家庭），表示"他们的"。 belts 是名词 belt 的复数形式，指"腰带、皮带"。 tighten their belts 是一个习语，字面意思是"勒紧腰带"，比喻在经济困难时期节约开支、减少消费。