A flat cake lifted straight off the hot pan, still steaming. Two things are true of it at once: it is food, and it will not stay on the plate for long, because people are already waiting for it. English keeps the first fact as the name of the food, and borrows the second one to talk about anything that is being bought too fast to keep up with.
可以想成剛從熱鍋上鏟起來的一片餅，還冒著煙。這個畫面同時有兩件事：它是食物，而且它不會在盤子上待太久，因為旁邊的人早就在等了。英文把第一件事留下來當這種食物的名字，再把第二件事借出去——形容一樣東西賣得快到補不上貨。要注意的是，第二個意思只活在 selling／going like hot cakes 這個說法裡。