The term twin flame refers to a single soul that is split into two halves. These two halves can vary in form including incarnating as two individual people.
Twin flames are often opposites in terms of their personalities, preferences, and experiences leading up to their reunion. This is done intentionally so that they can learn to fully accept each other and in the process accept the all that is. At the point of complete acceptance with one another, their soul reaches a state of balance which allows them to feel pure and complete.