Hallucination refers to something a person sees and/or hears that isn't real. Hallucinations can be symptoms of very many different illnesses. 
Religious visions also happen to very many people with very many different Religious beliefs. Christians see or hear whatever that's connected to Christianity, sometimes to their specific Denomination or sect, for example Roman Catholics sometimes report visions of Saints but Protestants see different visions. Hindus see visions connected with the Pantheon of Hinduism and so it goes on. Sometimes religious visions happen to people who clearly have medical problems but occasionally the people involved are in other respects sane and healthy.