What does the cryptic crossword clue "Welsh town's fashion, not posh (4)" mean?

The definition is "Welsh town's". The wordplay uses a deletion. MOLD (deletion) = MOLD; definition: "Welsh town's" The answer is MOLD.

Welsh town's fashion, not posh (4)

Guardian Cryptic #28972 | 13 Across | 2023-01-20 flower