Every single word and phrase; literally word for word—used to indicate that nothing is omitted.
彼は会議の内容を一言一句書き留めた。
He wrote down every single word of the meeting.
原稿は一言一句違わず本人の確認を受けた。
The manuscript was checked by the person so that not a single word differed.
彼女のスピーチを一言一句覚えている人は少ない。
Few people remember her speech word for word.
録音を使って一言一句を正確に書き起こした。
Using the recording, I transcribed every single word exactly.