1Number one: first place; the best or top-ranking person or thing. Common in speech and advertising.
彼はチームのナンバーワン選手だ。
He is the team's number-one player.
この商品は売上でナンバーワンになった。
This product became number one in sales.
ナンバーワンになりたいなら練習を続けるしかない。
If you want to be number one, you have to keep practicing.