It means they like eating sweets.
句意:当人们说他们有“a sweet tooth”时,这是什么意思?
根据第一段第一行:
Do you have a sweet tooth?Do you like chocolate very much?你有__吗?你非常喜欢巧克力吗?
可推测第一句表示你是否对巧克力这样的甜食感兴趣,结合tooth表示牙齿,故a sweet tooth与吃甜食有关,意为“爱吃甜食”,故答案为:
It means they like eating sweets.