During the holiday rush, the airport terminals were overflowing with weary travelers.

overflowing 是动词 overflow 的现在分词形式。overflow 由前缀 over-（表示"超过"）和动词 flow（流动）组成，字面意思是"流出来"，引申为"充满、溢出"。 在句中用现在分词形式表示航站楼当时"人满为患"的状态。