The Japanese noun 'リーダー (riidaa)' means 'leader'. It is a loanword from English, and it is used to refer to someone who leads or guides a group, team, or organization. This term is commonly used in both professional and casual contexts. For example: he is the leader of the team「彼はチームのリーダーです」(かれはチームのリーダーです). She became the leader of the project「彼女はプロジェクトのリーダーになりました」(かのじょはプロジェクトのリーダーになりました). The word can also refer to a person who is influential or a role model in a specific field.