Gairaigo
Gairaigo (kanji: 外来語, hiragana: がいらいご) are loanwords in the Japanese language from languages other than Old or Middle Chinese. The word itself literally means "loan word". Most gairaigo come from European languages, and especially English since the post-WWII era, though Modern Chinese and Modern Korean are also popular sources for loanwords. Most gairaigo nowadays are written in katakana, with some older ones being written in ateji (kanji used only to show a word's pronunciation and not its meaning) or even in hiragana. For example, while America, or Amerika in Japanese, can be written as 亜米利加 in ateji, it is rare to do so these days, and instead it is almost always written in katakana as アメリカ.