It means “Wheat straw” or “Barley straw” in English.
“Mugi” of the first character means “wheat” or “barley”, and “Wara” of the second character means “straw”.
Monkey D. Luffy is nicknamed “Straw Hat Luffy” (Mugiwara no Rufi) in ONE PIECE.
What is your favorite word in “ONE PIECE“? I’m waiting for a request.