Her teeth are quite gappy, with noticeable spaces between them when she talks.

gappy 是由名词 gap（缝隙、缺口）加上形容词后缀 -y 构成的形容词，意思是"有缝隙的、有缺口的"。gappy teeth 指牙齿之间有明显缝隙的状态，即"牙齿稀疏"。