Repressive things keep people from doing or saying what they want. Repressive controls on the press don't allow journalists to freely report the news.
It's almost always a government, or a political or social system, that acts in a repressive way. When police officers don't let citizens videotape arrests, or a society doesn't allow girls to attend school, it's repressive. Someone growing up in a repressive family might feel cautious about saying or doing the wrong things. The adjective repressive comes from the Latin root repressus, "held back or curbed," and also "checked or restrained."