When the Catholic Church uses that term, it is refering the age at which a person is permitted to enter into the Sacrament of Holy Matrimony as sexual intercourse is not condoned outside of marriage. It can be either as a right or subject to parental or other forms of consent. Age and other prerequisites to marriage vary from one jurisdiction to another, but generally is set at about eighteen. Most jurisdictions allow marriage at a younger age with parental or judicial approval, and some also allow younger people to marry if the girl is pregnant. The marriage age should not be confused with the age of majority, though in some places they may be the same.
In secular society the age of consent can be that age at which a minor is legally permitted, without regard to marital status, to have sexual intercourse, but that is outside of the Church as premarital sex is not condoned.