It is a noun/an adjective verb and it means "to be diligent". It is used when describing someone who spares no effort to work hard or to care for other people.
- Meg : Do you talk to your boyfriend every day?
毎日彼氏と話している? - Amy : Yes. It's been three months since we started a long-distance relationship, but he texts me every night to know if I'm doing well. He is very caring and gentle.
うん。遠距離恋愛を始めてから三カ月経つけど、毎日連絡くれるよ。すごくまめなの。 - Meg : You're lucky. My boyfriend lives nearby, but he rarely texts me.
いいな。私の彼氏なんて近所に住んでいるのに、めったに連絡くれない。
- Ken : It's time to go home. When are you leaving?
帰らなきゃ。レオは何時に終わる(or帰る)の? - Leo : I'm going to leave before 11 pm so I can catch the last train.
終電には間に合うように、11時までには出るよ。 - Ken : You never cut corners at work. You're such a diligent person.
レオは全く手を抜かないよね。まめだよね(orまめに働くよね)。 - Leo : I just want this project to be successful.
ただこのプロジェクトを成功させたいだけだよ。