-女性 means "female", used more for sexual distinction between male & female. Like: 女性の学校 (School for females) -彼女: Lireraly, means "She" or "Girlfriend". You can only use it as a 3rd person singular feminine pronoun, or to talk about your girlfrient. -女: Simply means "woman". It can be used also as 女たち to express specifically "women", but Japanese usually doesn't care about plural and singular distinctions. 女の人: To adress a "woman" solely as 女 may sound rude and very informal. That is why we use 女の人. So if you want to express: "That woman is my friend" ... then you would say: "あの女の人は私の友達です". 女の子: 子 means "kid" or "child", so it is used for " young girl".