A transliteration requirement means the trademark application includes characters from a non-Latin script; such as Arabic, Chinese, Cyrillic, Hebrew, or Japanese; and the USPTO is requesting a transliteration of those characters into the Latin alphabet.
Though they’re often confused, transliteration is different from translation. Translation renders the meaning in English, while transliteration renders the pronunciation using Latin characters. The USPTO sometimes requests both if your mark includes non-Latin characters. To successfully respond, submit the transliteration and, if required, the translation. The process is typically straightforward and does not incur any government fees.