A word adopted from another language, such as “ballet” in English, is called a loanword.
Loanwords enter a recipient language through contact between speakers. English has borrowed extensively from French, Latin, Norse, Arabic, Hindi, Spanish, Italian, Japanese, and many other languages. Ballet is associated with French, while café, bazaar, kindergarten, and karaoke illustrate other borrowing routes.
The term “loan” is metaphorical: the donor language does not lose the word, and the recipient language does not return it. Once adopted, a loanword may change its spelling, pronunciation, grammar, or meaning. Some become so familiar that speakers no longer recognize them as foreign.
A loanword differs from a calque, or loan translation. English adopts the form of a loanword, but translates the components of a calque into existing words or roots. Loanwords also differ from cognates, which resemble one another because they descend from a shared ancestor rather than because one language borrowed directly from the other. English’s large borrowed vocabulary reflects its long history of cultural contact.