薄 is thin, and 餅 refers specifically to Chinese wheat flour breads, but also generally to flat and circular foods like cakes and cookies (and not just foods, e.g. a discus is an iron pancake, 鐵餅 tit béng). So 薄餅 is thin pancake.
Thin wheat flour pancakes. These are often used as wrappers with fillings, including Chinese-American mushu dishes, but also by themselves (sometimes listed as roti).