Although not a classical definition, Wikipedia seems also to have generally open-ended definition for a miracle:
A miracle is a supernatural event that seems inexplicable by natural or scientific laws. In various religions, a phenomenon that is characterized as miraculous is often attributed to the actions of a supernatural being, (especially) a deity, a magician, a miracle worker, a saint, or a religious leader
The Catholic Church believes miracles are works of God, either directly, or through the prayers and intercessions of a specific saint or saints. There is usually a specific purpose connected to a miracle, e.g. the conversion of a person or persons to the Catholic faith or the construction of a church desired by God. The Church says that it tries to be very cautious to approve the validity of putative miracles. The Catholic Church says that it maintains particularly stringent requirements in validating the miracle's authenticity. The process is overseen by the Congregation for the Causes of Saints.
For a majority of Evangelical Christians, biblicism ensures that the miracles described in the Bible are still relevant and may be present in the life of the believer. Healings, academic or professional successes, the birth of a child after several attempts, the end of an addiction, etc., would be tangible examples of God's intervention with the faith and prayer, by the Holy Spirit. In the 1980s, the neo-charismatic movement re-emphasized miracles and faith healing. In certain churches, a special place is thus reserved for faith healings with laying on of hands during worship services or for campaigns evangelization. Faith healing or divine healing is considered to be an inheritance of Jesus acquired by his death and resurrection.
The most basic and classic definition of a miracle would be as follows:
