each person; each mouth; one after another
Usually used as 口々に, describing many people saying something separately, in turn, or all voicing their own words.
See also: 口々に
Everyone expressed their thanks one after another.
The audience members praised the performance one after another.
each entrance; every opening
A much less common literal extension of 口 meaning an entrance or opening; in modern everyday Japanese, 各入口 or 入口ごと is usually clearer.
If an old account says 'secure the kuchiguchi of the castle,' it means guarding each entrance of the castle.
The audience each said, in their own words, that they were moved.
The residents each voiced their complaints one after another.
The children each shouted "Teacher!" at once.