It means “Three‐sword fencing” in English.
“San” of the first character means “Three”, “Tou” of the second means “Sword”, and “Ryu” of the last means “Style”.
Roronoa Zoro is the swordman of “Santou-Ryu” in ONE PIECE.
In Japan, the great swordsman “MIYAMOTO Musashi” (1584?-1645) is the most famous for two-sword fencing.
What is your favorite word in “ONE PIECE”? I’m waiting for a request.