A brainfart (also written brain fart, two words) is a sudden blank in the mind, especially when you are already talking: the next word, a name, a number is sitting there, and then, for a second, it is gone. You stop mid-sentence, you look a little silly, and it often comes back. Informal, and a bit crude, because fart is a bathroom word — fine with friends, not for a test, a teacher, or a job email. It does not mean you are stupid. Even careful speakers have one. People also stretch it to any short slip: walking into a room and forgetting why, saying Wednesday when you mean Tuesday. Though actually, the core picture is that short “pop” of emptiness, not a person who never thinks. It is also not brain freeze, which is the sharp headache some people get from a cold drink.

突然忘詞；腦袋當機（說話說到一半卡住。口語，有 fart「放屁」，有點粗）。不是說這個人一直很笨。