Ahava rabba, or “great love,” is “higher” love. Chassidus usually (if not always) defines love as a longing, yearning, desire, attraction, to be one.
Ahava rabba, as with all emotions, is a result of will. Will is a result of contemplation and the contemplation is on that which is beyond understanding. For example: one may think about the fact that G-d cannot be understood, or that there is no place where He is not, etc.
This type of love is characterized by tzaddikim who have no urge fire anything unholy.
See Ahavas Olam.