Holiday pounds refer to the extra little bit of weight you put on during a period of being on holiday or vacation.

Holiday pounds指休假或者節假日期間額外增長的那部分體重，大家可以戲稱為假期胖子。

For example:

Man, when I get back to work Ill have to start going to the gym again- Ive put on some serious holiday pounds.

唉，等我回去上班，我得開始去健身俱樂部了，休假長了不少肉。