In Buddhism: the 'mouth' or speech aspect — the verbal expression or teaching (one of the three mysteries).
三密では、身・口・意の口は仏語を説く側面を指す。
In the three mysteries, the 'mouth' (kuchi) refers to the aspect of the Buddha that speaks the teachings.
法要で僧が『口を開く』と言うとき、それは説法を行う意味だ。
When a monk says he will 'open his mouth' at a ceremony, it means he will give a sermon.
A suffix/counter (～口) used to count people, shares, or implements; usually read as こう in some compounds.
一口（一こう）千円の出資を募っています。
We are asking for investments of one share (ikkō) worth 1,000 yen each.
この魚は一口で食べられるサイズだ。
This fish is bite-sized (one mouthful).
配当は株主一口につき50円支払われた。
A dividend of 50 yen was paid per share (per unit).