What does the cryptic crossword clue "Part of France which Esio Trot 's first name comes from? (4)" mean?

The definition is "Part of France". The wordplay uses an anagram. anagram of ESIO = OISE; definition: "Part of France" The answer is OISE.

Part of France which Esio Trot 's first name comes from? (4)

Independent Cryptic #11771 | 19 Across | 2024-07-02 flower