It means "mouth"(miệng). Actually it's the Han-Viet equivalent for the Vietnamese "miệng". Context would help here because I believe there's more than one way to translate it.
Khẩu is an element (morpheme to be precise) meaning "mouth, door". It's a Sino-Vietnamese morpheme so it's never exist on its own as a word. It is used with other morphemes to create words.
For example, "khẩu vị" = "mouth" + "taste" = appetite.
"nhập khẩu" = "inward" + "door" = import
In addition, if "Khẩu" is used with some particular words, they will become new words with distinct meanings.
For instance, "Khẩu súng" : a gun
" Khẩu độ" : aperture (technical specification of camera)