What is the Japanese writing system used for foreign words?

The Japanese writing system used for foreign words is katakana.

Katakana is a syllabary, meaning its symbols generally represent sounds or morae rather than individual meanings. Modern Japanese uses it especially for gairaigo, or loanwords adopted from other languages. For example, “television” is テレビ (terebi), and “coffee” is コーヒー (kōhī).

Katakana also writes foreign personal names, place names, onomatopoeia, scientific terms, and words that need emphasis. It can approximate sounds Japanese does not traditionally have, using combinations such as ファ (fa) and ティ (ti).

Katakana and hiragana are both kana systems, but they have different usual roles. Hiragana is common for grammatical endings and many native Japanese words, while kanji carries meaning in many native and Chinese-derived terms. Rōmaji is not a Japanese kana script: it is the use of Latin letters to represent Japanese.