Or rather, Sternberg’s Triangular Love Scale (STLS).
The theory is that love can be understood in terms of three components; intimacy, passion and decision/commitment.
Intimacy. Intimacy refers to feelings of closeness, connectedness, and bondedness in loving relationships. It thus includes within its purview those feelings that give rise, essentially, to the experience of warmth in a loving relationship.
Passion. Passion refers to the drives that lead to romance, physical attraction, sexual consummation, and related phenomena in loving relationships. The passion component includes within its purview those sources of motivational and other forms of arousal that lead to the experience of passion in a loving relationship.
Decision/commitment. Decision/commitment refers, in the short-term, to the decision that one loves a certain other, and in the long-term, to one’s commitment to maintain that love. These two aspects of the decision/commitment component do not necessarily go together, in that one can decide to love someone without being committed to the love in the long-term, or one can be committed to a relationship without acknowledging that one loves the other person in the relationship.
Nonlove refers simply to the absence of all three components of love. Liking results when one experiences only the intimacy component of love in the absence of the passion and decision/commitment components. Infatuated love results from the experiencing of the passion component in the absence of the other components of love. Empty love emanates from the decision that one loves another and is committed to that love in the absence of both the intimacy and passion components of love. Romantic love derives from a combination of the intimacy and passion components. Companionate love derives from a combination of the intimacy and decision/commitment components of love. Fatuous love results from the combination of the passion and decision/commitment components in the absence of the intimacy component. Consummate, or complete love, results from the full combination of all three components.
And research now indicate that it is reproducible across cultures. I find this surprising, as I had the idea that love had evolved together with human cultural development but apparently I was wrong.