The word "马匹" is a collective noun formed through a common Chinese lexical pattern where a specific noun ("马," meaning *horse*) is combined with its associated generic measure word ("匹," the classifier for horses). This construction transforms a singular, countable concept into a plural or general term referring to the category as a whole. Thus, "马匹" does not mean "one horse" but rather "horses" in a collective sense, emphasizing the grouping or category itself, much like how "车辆" (车 + measure word 辆) means "vehicles" or "纸张" (纸 + measure word 张) means "paper."