A person who is the exact same as you i.e same intrests, same type of family, same birthday, same pets. This would make the person your twin, but if you dont look anything alike it makes the person your spiritual twin. A spiritual twin is likely to share the same thoughts as you, and you are likely to "jinx" eachother on a regular basis.
Person 1:"My best friend is my twin."
Person 2: "but you dont look like twins?"
Person 1:"thats cause shes my Spiritual Twin!"
Person 2: "i now understand this concept completely"