1. section (i.e. of text); sentence; passage; paragraph
彼は聖書の句を引用した。He quoted a passage from the Bible.
2. phrase
文でもなければ句でもない。It's neither a sentence nor a phrase.
3. verse (of 5 or 7 mora in Japanese poetry; of 4, 5, or 7 characters in Chinese poetry)
短歌は五つの句からできている。A tanka is made up of five verses.
4. haiku; first 17 morae of a renga, etc.
旅先で句を詠むのが趣味だ。My hobby is composing haiku when I travel.
5. maxim; saying; idiom; expression
「急がば回れ」という句を思い出した。I remembered the saying 'More haste, less speed.'
6. clause (e.g. in a database query language)