The leading part or leading actor/actress; the main role in a play, film, or story.
彼女がこの映画の主役を演じる。
She will play the leading role in this movie.
舞台では主役と脇役の掛け合いが見どころだ。
On stage, the interplay between the lead and supporting roles is the highlight.
パーティーの主役は誕生日を迎えた友人だ。
The person of honor at the party is the friend who has a birthday.