Otona (大人) means "adult." It refers to a mature person, typically someone who has reached full physical and mental development, or legal age. It is the antonym of "kodomo" (child) and is used when distinguishing between adults and children. Example: 彼はもう大人です。(Kare wa mō otona desu.) = He is already an adult.

成熟した人間を指す言葉で、「子供」の反対です。例：彼はもう大人です。